PORTABLE NO-PUMP MULTI-FUEL STOVE Technical Field [1] The present invention relates to a portable no-pump multi-fuel stove in which a gasoline injection hole is devised to have multi functions so as to enable injection of butane as well as gasoline and also to act as a check valve and a safety valve in combination. [2] In addition, a preheating tube installed to traverse an upper portion of a burner bowl has a dual structure so that a gas tube with small diameter is inserted into the preheating tube as a gas passage and an inhaling member is put into a space out of the preheating tube. [3] Thus, gas is injected into the preheating tube and fuel in a liquid state is injected out of the preheating tube. Multiple heat sinks are provided to an inner upper end of a fuel tank at intervals so that conductive heat of the burner bowl may directly heat the inner upper end of the fuel tank. [4] Thus, a pressure of the expanded gas allows fuel to be continuously injected without any pressuring work. Accordingly, butane gas is injected in advance at an ignition stage so as to be injected and combusted through a nozzle of a main valve via the gas tube in the dual preheating tube after passing through an upper end of the fuel tank, thereby eliminating a conventional problem of incomplete combustion of gasoline caused by preheating. [5] In addition, once a certain amount of butane is combusted, though butane is not supplied, gasoline is continuously inhaled, vaporized and injected by means of the pressure vapor expanded by conductive heat of the heat sinks multiply installed to the inner upper end of the fuel tank at intervals and also by means of osmotic pressure of the inhaling member in the dual preheating tube without any pressuring work for the gasoline. [6] In addition, since a single groove is formed vertically on an outer side of a fuel injection screw, gas is discharged downward only when the fuel cap is turned for reducing an inner pressure of the fuel tank after the stove is used. The present invention also relates to such a portable no-pump no-preheating self-pressure multi- fuel stove with small and light structure. Background Art [7] Generally, a portable stove is a device frequently used for cooking in outdoor leisure activities such as mountain climbing, fishing or the like. The stove is in brief classified into petroleum or gasoline stoves using atomized or vaporized liquid fuel, and gas stoves using liquefied gas fuel (butane). However, the petroleum stove needs a preparation tool for preheating such as a preheating torch and alcohol, which is so cumbersome. In addition, due to high risks in preheating, the petroleum is gradually used not so often. [8] Meanwhile, the gas stove using butane as a fuel is recently widely used owing to convenience in carriage and manipulation. However, the gas stove gives small energy output in comparison to volume of liquefied butane, and its flame is easily ex¬ tinguished by wind. In addition, due to the high evaporation point (e.g., - 0.5 0C for butane), fuel is not sprayed in below-zero temperature, so it can be hardly used in the winter unless a separate heating device is attached thereto. Moreover, propane gas is not suitable for a portable stove since it requires very strong container to endure pressure due to its too low evaporation point (- 40 0C). [9] In contrast, the gasoline stove does not need any separate tool for preheating since gasoline itself gives the preheating action, and also the gasoline stove gives better heating power than the gas stove. In addition, since gasoline is in a liquid state, it is easy to supplement fuel as required at any time without exchanging a container, differently from the stove using butane gas. [10] In addition, the gasoline stove ensures easy ignition even in below-zero temperature or against the wind, so it is convenient to use. However, a conventional gasoline stove has a problem that a preheating tube is insufficiently heated at an initial ignition so that gasoline is incompletely combusted in a liquid state. [11] Thus, the gasoline stove should endure an unnecessary preheating process, which causes generation of black dirt and spreading of red flame, until the preheating tube is sufficiently preheated to reach a complete combustion state at which gasoline is vaporized and gives flue flame. In addition, a pressure pump is required for filling up an external air into a fuel tank when an internal pressure of the fuel tank is decreased in use or due to consumption of fuel. This pump should be frequently repaired and exchanged due to a worn packing or the like. Furthermore, the pump increases weight of the stove and is also not preferable in an economic view since it is a factor of price increase by about 20 to 30%. Disclosure of Invention Technical Problem [12] The present invention is designed to solve the problems of the prior art, and [13] therefore an object of the invention is to provide a portable stove using both gasoline and gas without a pump, which may be used as a gasoline stove or a gas stove as required by making a preheating tube in a dual structure, eliminate a preheating process and resultant unnecessary energy consumption by injecting and combusting butane gas at an initial ignition state when being used as a gasoline stove, and also allow a fuel to keep vaporized and injected without any pressuring work after ignition. [14] Another object of the invention is to provide a portable stove using both gasoline and gas without a pump, in which a plurality of heat sinks heated by heat conducted from a heating unit are multiply installed at intervals so that an inner gas in a fuel tank is expanded using a heat radiated from the heat sinks and thus an air pressure is increased, thereby not requiring any separate pressuring work and ensuring good combustion. [15] Still another object of the invention is to provide a portable stove using both gasoline and gas without a pump, in which a fuel map is devised to have multi functions to act as a check valve and a safety valve, and a butane gas connector may be detachably attached to the top of the fuel cap by means of one touch. [16] Further another object of the invention is to provide a portable stove using both gasoline and gas without a pump, which may prevent accidents by configuring so that a high temperature gas in the fuel tank is discharged downward toward the ground when a fuel cap is separated from the stove after the stove is used. Technical Solution [17] In order to accomplish the above object, the present invention provides a portable no-pump multi-fuel stove, in which a burner bowl acting as a windscreen, a flame hole ring where at least one ply of a flat flame hole ring and a flame hole ring with a V- shaped groove are accumulatively assembled, and a burner cap are subsequently assembled to a central upper portion of a fuel tank having a cylindrical shape with a fuel injection hole to which a fuel cap is combined so that a tripod is attached to an outer side of the fuel tank, a gas injection hole, a check valve and a safety valve are installed to a side upper portion of the fuel tank, a preheating tube is installed to traverse an upper portion of the burner bowl, a flame control valve having a nozzle is formed at a front end of the preheating tube, and the flame control valve is connected to a guide tube having a front end fixed to an inner bottom of the burner bowl, wherein the gas injection hole, the check valve and the safety valve are installed to an inside of the fuel cap, wherein the preheating tube is composed of a dual preheating tube so that a gas tube having a predetermined diameter is inserted in the dual preheating tube, one end of the gas tube being communicated with an upper space of the fuel tank, the other end of the gas tube being communicated with the flame control valve, wherein an inhaling member is filled into a space out of the gas tube within the dual preheating tube so as to be contacted with an inner bottom of the fuel tank, wherein a rod for supporting the burner cap and transferring heat is penetrated into an upper inside of the fuel tank so that at least one heat sink is attached to the rod in multi stages at suitable intervals. [18] Here, the heat sink preferably has a smooth plate shape or a waved shape that gives a relatively larger heat emitting area. The heat sink is preferably made of copper or alloys thereof. Preferably, a control valve support whose lower end is contacted with an upper outer surface of the fuel tank and upper end is contacted with an outer bottom of the burner bowl is integrally installed to a rear end of the guide tube. [19] A filter for removing impurities is preferably installed to an end of the inhaling member toward the flame control valve. The inhaling member may be made of one selected from the group consisting of silicate fabric woven with silicate yarns, metal fabric composed of a plurality of metal fibers, glass fiber and rock wool. [20] The fuel injection hole preferably has a gas discharge hole additionally formed in one side positioned in a lower portion so that a high pressure gas in the fuel tank is discharged downward toward the ground when the fuel cap is separated after the stove is used. [21] Preferably, the dual preheating tube has a diameter that is constant over the entire length, or that is greatest at a portion toward the fuel tank and gradually decreased toward the flame control valve. [22] The inhaling member filled in the outer space of the gas tube within the dual preheating tube is preferably filled from an inner bottom of the fuel tank up to a top of an overall length of the dual preheating tube or up to a middle portion. [23] The flame control valve preferably includes a pipe having a screw on an inside of one end thereof; a body positioned in the pipe to be screwed to the screw of the pipe, the body having a large diameter portion at a middle portion so that an end of the inhaling member toward the flame control valve is opened or closed when the body moves right or left; and a detachable nozzle cleaning device screwed to the other end of the body and having a nozzle hole and an inner space so that the nozzle is detachably mounted to the nozzle hole and the inner space, wherein the nozzle has one end bent so that the bent end is positioned in the inner space of the detachable nozzle cleaning device, and the nozzle has the other end protruded through the nozzle hole so that the screwed detachable nozzle cleaning device is not separated from the body of the flame control valve. [24] The dual preheating tube connected to the flame control valve is preferably configured so that its one end has an inner diameter smaller than the other end. In addition, the pipe of the flame control valve is preferably configured so that one end thereof is enlarged more than the other end, whereby a bushing, a gasket seal and a packing fastening bolt are put around the body to fill the space formed around the body for the purpose of keeping an airtight and waterproof state. Advantageous Effects [25] Therefore, the stove of the present invention may use gasoline and butane together. In particular, butane gas is injected into the fuel tank in a region above gasoline so that the butane gas is combusted at an initial ignition stage, thereby eliminating the need of preheating that results from incomplete combustion of gasoline at an initial ignition stage in a conventional gasoline stove. [26] In addition, once a certain amount of butane is combusted, though butane is not supplied, gasoline is continuously inhaled, vaporized and injected by means of vapor pressure in an upper portion of the fuel tank and osmotic pressure of the inhaling member without any pressuring work for the gasoline. [27] In addition, the present invention ensures the nozzle to be not easily separated but easily exchanged. Moreover, the gas discharge hole is formed downward at one side of the fuel injection hole, and the inhaling member is filled to a middle portion of the entire length of the preheating tube, so that the portable multi-fuel stove may have small and light structure. Brief Description of the Drawings [28] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings; [29] Fig. 1 is a perspective view showing a stove according to a preferred embodiment of the present invention; [30] Fig. 2 is a longitudinal sectional view of Fig. 1; [31] Fig. 3 is a front view showing that a flame hole ring with a V-shaped groove and a flat flame hole ring are accumulatively assembled between a burner cap and a burner bowl of the stove shown in Fig. 1; [32] Fig. 4 is a detailed view showing a dual preheating tube according to a preferred embodiment of the present invention; [33] Fig. 5 is a detailed view showing a dual preheating tube according to another embodiment of the present invention; [34] Fig. 6 is a sectional view of the dual preheating tube, taken along the line A-A' of Fig. 4 and the line B-B' of Fig. 5; [35] Fig. 7 is a sectional view of the dual preheating tube, taken along the line C-C of Fig. 5; [36] Fig. 8 is a detailed sectional view showing that an end of an inhaling member toward a flame control valve is closed according to a preferred embodiment of the present invention; [37] Fig. 9 is a detailed sectional view showing that an end of an inhaling member toward a flame control valve is opened according to a preferred embodiment of the present invention; [38] Fig. 10 is a schematic view showing that the stove according to one embodiment of the present invention is connected to an external gas injection means; and [39] Fig. 11 is a sectional view showing that the stove according to one embodiment of the present invention is received in a case. Best Mode for Carrying Out the Invention [40] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. [41] Fig. 1 is a perspective view showing a stove according to a preferred embodiment of the present invention, Fig. 2 is a longitudinal sectional view of Fig. 1, and Fig. 3 is a front view showing that a flame hole ring with a V-shaped groove and a flat flame hole ring are accumulatively assembled between a burner cap and a burner bowl of the stove shown in Fig. 1. [42] As shown in Figs. 1 to 3, a portable stove 100 using both gasoline and gas according to a preferred embodiment of the present invention is configured so that a burner bowl 5 acting as a windscreen, a flame hole ring 6 where at least one ply of a flat flame hole ring and a flame hole ring with a V-shaped groove are accumulatively assembled, and a burner cap 7 are subsequently assembled to a central upper portion of a fuel tank 4 having a cylindrical shape with a fuel injection hole 2 to which a fuel cap 1 is combined so that a tripod 3 is attached to an outer side of the fuel tank 4, a gas injection hole Ia, a check valve Ib and a safety valve Ic are installed to a side upper portion of the fuel tank 4, a preheating tube is installed to traverse an upper portion of the burner bowl 5, a flame control valve 10 having a nozzle 9 is formed at a front end of the preheating tube, and the flame control valve 10 is connected to a guide tube 11 having a front end fixed to an inner bottom of the burner bowl 5. At this time, the gas injection hole Ia, the check valve Ib and the safety valve Ic are installed to an inside of the fuel cap 1. [43] The preheating tube is composed of a dual preheating tube 8 so that a gas tube 13 having a predetermined diameter is inserted in the dual preheating tube 8, one end of the gas tube 13 being communicated with an upper space of the fuel tank 4, the other end of the gas tube 13 being communicated with the flame control valve 10. In addition, an inhaling member 14 is filled into a space out of the gas tube 13 within the dual preheating tube 8 so as to be contacted with an inner bottom of the fuel tank 4. In addition, a rod 28 for supporting the burner cap and transferring heat is penetrated into an upper inside of the fuel tank 4 so that at least one heat sink 29 is attached to the rod 28 in multi stages at suitable intervals. Mode for the Invention [44] To describe the stove in more detail, the gas injection hole Ia, the check valve Ib and the safety valve Ic are installed in the fuel cap 1. At this time, an upper piston and a lower piston respectively supported by an upper spring with a relatively stronger force and a lower spring with a weaker force than the upper spring are installed to both ends of a piston rod that passes through a lateral partition plate. A gas hole 12 is formed between positions of the lower spring when being extended and when being contracted by way of well-known configuration. [45] When butane gas or air is pressed or injected from an upper position, the lower piston with a relatively weaker force is descended so that the butane gas or the air may be introduced into the fuel tank 4 through the gas hole 12 without flowing backward. In addition, if reverse pressure is excessively applied from the inside of the fuel tank 4 since the gas in the fuel tank 4 is heated while gasoline is combusted, the internal gas fills a space where the gas injection hole Ia, the check valve Ib, the safety valve Ic and the lower spring are installed, and then the internal gas pushes up the upper piston by means of the lower piston and the piston rod so as to be discharged out, thereby solving the excessive reverse pressure that is a function of a safety valve. Thus, the gas injection hole Ia, the check valve Ib and the safety valve Ic installed in the fuel cap 1 facilitates easy repair and exchange and allows a connector 21 tube to be easily combined thereto from outside. [46] Fig. 4 is a detailed view showing a dual preheating tube according to a preferred embodiment of the present invention, Fig. 5 is a detailed view showing a dual preheating tube according to another embodiment of the present invention, Fig. 6 is a sectional view of the dual preheating tube, taken along the line A-A' of Fig. 4 and the line B-B' of Fig. 5, and Fig. 7 is a sectional view of the dual preheating tube, taken along the line C-C of Fig. 5. [47] As shown in Figs. 4 and 6, the inhaling member 14 filled in the outer space of the gas tube 13 within the dual preheating tube 8 may be filled from an inner bottom of the fuel tank 4 up to a top of an overall length of the dual preheating tube 8. However, it is also satisfactory that the inhaling member 14 is filled up to a middle portion as shown in Figs. 5 and 7. If the stove 100 is ignited after butane gas is sufficiently injected into the fuel tank 4, the butane gas filled in the fuel tank 4 is ejected to the nozzle 9 of the flame control valve 10 through the gas tube 13 installed to the dual preheating tube 8 and then combusted prior to gasoline. While the butane gas is combusted, the dual preheating tube 8 and the flame control valve 10 are sufficiently preheated. Thus, just after the butane filled in the fuel tank 4 is all combusted, gasoline is fully vaporized via the inhaling member 14 by means of osmotic pressure though the gasoline is sucked up to a middle portion of the entire length of the dual preheating tube 8 from the inside of the fuel tank 4. [48] The dual preheating tube 8 may have a diameter that is constant over the entire length. However, it is also possible that the dual preheating tube 8 has a diameter that is greatest at a portion toward the fuel tank 4 and gradually decreased toward the flame control valve 10. [49] In addition, the dual preheating tube 8 may employ a flexible tube that is easily bent, so as to facilitate easier bending work when the dual preheating tube 8 is fabricated. [50] The inhaling member 14 is preferably made of silicate fabric woven with silicate yarns or metal fabric composed of a plurality of metal fibers. It is because the gasoline in a liquid state may be rapidly sucked up to the flame control valve 10 from the inside of the fuel tank 4 by means of osmotic pressure and also the inhaling member 14 may endure high pressure of the flame transferred through the dual preheating tube 8 in the case that the stove of the present invention is used as a gas stove. Of course, it is also possible to use silicate fabric and metal fabric together so that the inhaling member is made of silicate fabric up to a middle portion of the dual preheating tube 8 and also made of metal fabric in the other portion. Meanwhile, glass fiber and rock wool may be also used as a material of the inhaling member 14, in addition to silicate fabric or metal fabric mentioned above. [51] Fig. 8 is a detailed sectional view showing that an end of an inhaling member toward a flame control valve is closed according to a preferred embodiment of the present invention, and Fig. 9 is a detailed sectional view showing that an end of an inhaling member toward a flame control valve is opened according to a preferred embodiment of the present invention. [52] As shown in Figs. 8 and 9, the flame control valve 10 includes a pipe 10a having a screw 30a on an inside of one end thereof, a body 30 positioned in the pipe to be screwed 30a to the screw of the pipe and having a large diameter portion 34 at a middle portion so that an end of the inhaling member 14 toward the flame control valve 10 is opened or closed when the body 30 moves right or left, and a detachable nozzle cleaning device 31 that may be screwed to the other end of the body 30 and has a nozzle hole and an inner space so that the nozzle 9 is detachably mounted to the nozzle hole and the inner space. [53] Here, the nozzle 9 has one end bent to be combined in correspondence to the screw of the pipe so that the bent end is positioned in the inner space of the detachable nozzle cleaning device 31 and may be screwed with the screw of the pipe. In addition, the other end of the nozzle 9 has a screw to be screwed to the screw of the detachable nozzle cleaning device 31. In addition, the body 30 has a certain gap between the body 30 and the inner circumference of the pipe. Through the gap, a fuel inhaled from the end of the inhaling member 14 toward the flame control valve 10 may be injected. [54] In addition, the body 30 has the large diameter portion 34 at its middle portion. The large diameter portion 34 may close the end of the inhaling member 14 toward the flame control valve 10 as shown in Fig. 8. When the body 30 is rotated to move right as shown in Fig. 9, the large diameter portion 34 formed at the middle portion of the body 30 is moved together. Thus, the closed end of the inhaling member 14 toward the flame control valve 10 may be communicated with the gap formed between the outer circumference of the body 30 and the inner circumference of the pipe. [55] The nozzle 9 is bent so that its bend portion is positioned in the inner space of the detachable nozzle cleaning device 31 and a front end of the nozzle 9 is protruded through the nozzle hole. Thus, when the detachable nozzle cleaning device 31 is screwed to the body 30 of the flame control valve 10, it is prevented that the nozzle 9 is separated from the body 30. [56] The pipe of the flame control valve 10 is configured so that its one end is enlarged more than the other end. By using this configuration, a space is formed between the pipe and the body 30. In addition, a bushing 32, a gasket seal 33 and a packing fastening bolt 10a' are put around the body 30 to fully fill the space formed between the pipe and the body 30 so as to keep an airtight and waterproof state. A groove is formed on an outer portion of one end of the body 30, and a handle 30' is inserted to the groove so that a user may conveniently rotate the body right or left with escaping direct thermal contact. [57] In addition, a filter 16 is preferably installed to a portion of the flame control valve 10, which is combined to the dual preheating tube 8. The filter 16 filters impurities included in gasoline so that the nozzle 9 of the flame control valve 10 is not clogged due to black dirt generated by incomplete combustion of the impurities or the heating power of the stove 100 is not deteriorated. [58] At least one heat sink 29 are laterally attached in multi stages at suitable intervals to the rod 28 for supporting the burner cap and transferring heat, which is penetrated through an upper inside of the fuel tank 4. The heat sink 29 may have a smooth surface. However, it is also possible that the heat sink 29 has a waved surface by wrinkling so as to maximize a heat radiation area. In addition, the burner cap supporting and heat transferring rod 28 and the heat sink 29 may be made of materials with excellent thermal conductivity such as copper or its alloy, not limitedly. [59] A control valve support 15 whose lower end is contacted with an upper outer surface of the fuel tank 4 and upper end is contacted with an outer bottom of the burner bowl 5 may be additionally integrally installed to a rear end of the guide tube 11. Thus, the heat of the combustion flame is conducted into the fuel tank 4 through the burner bowl 5, the control valve support 15 and the upper surface of the fuel tank 4 so that heat is additionally supplied to the gas in the fuel tank 4. Resultantly, it makes the gasoline vaporized and injected at the nozzle 9 of the flame control valve 10 in better way. [60] The control valve support 15 also acts for supporting a rear of the guide tube 11. The gas tube 13 and the control valve support 15 are preferably made of material with excellent thermal conductivity such as copper or its alloy for heating the fuel tank 4 by means of thermal conductivity, like most components of the stove 100. [61] The flame hole ring 6 is configured as well known in the art so that a flat flame hole ring 6a, a flame hole ring 6b with a V-shaped groove, a flat flame hole ring 6c and a flame hole ring 6d with a V-shaped groove are stacked in order between the burner cap 7 and the burner bowl 5, as shown in Fig. 1. The stacked flame hole rings may guide flame dispersively in all directions by using multiple holes formed in a lateral direction, and also ensures the flame not to be directly contacted with burner cap 7, thereby reducing noise in combustion. The flat flame hole ring 6a and the flame hole ring 6b with a V-shaped groove may be stacked in single ply, or in multiple plies. [62] Meanwhile, there may be used a case 26 for receiving the multi-fuel stove according to the present invention for storage and carriage. The case 26 may have a body and a cover that have kocher and fryer shapes and their surfaces may be treated in a suitable way so that the body and the cover may be used instead of a kocher and a fryer. It may reduce weight of burdens for outdoor leisure activities. [63] In this case, butane is filled in the fuel tank 4 to press petroleum or gasoline in the tank. In addition, at an initial state, the dual preheating tube 8 is preheated since butane is combusted. After butane is all combusted, petroleum or gasoline is sufficiently vaporized through the dual preheating tube 8, thereby allowing complete combustion from the initial ignition. [64] In addition, in case of using butane, a butane gas connector is combined to the fuel cap 1 to inject butane, and then the stove is ignited. At this time, butane injected into the fuel tank 4 is continuously supplied to the nozzle 9 through the gas tube 13. In addition, the combustion heat generated here heats the dual preheating tube 8 positioned above the burner bowl 5, so petroleum or gasoline flowing through the preheating tube 8 is preheated. [65] Thus, if a certain amount of butane is combusted, the stove is ignited again with petroleum or gasoline as a source. However, since petroleum or gasoline is already preheated, it may be completely combusted from the ignition. [66] In order to ensure petroleum or gasoline to be continuously combusted without being extinguished, the internal pressure in the fuel tank 4 that presses fuel should be high. Though a pump was conventionally used for pressing inside of the fuel tank 4 frequently, the stove according to the preferred embodiment of the present invention does not require such a pressing process but increases the internal pressure of the fuel tank 4 by use of the combustion heat. That is to say, as mentioned above, the burner bowl 5 and the burner cap 7 are installed to the upper portion of the fuel tank 4 and they are also fixed to the burner cap supporting and heat transferring rod 28 inserted into the fuel tank 4. In addition, a plurality of the heat sinks 29 are also installed to the burner cap supporting and heat transferring rod 28 protruded above the fuel tank 4. Thus, if the fuel ejected through the nozzle is ignited, the burner cap 7 and the burner bowl 5 are heated, and the heat of the burner cap 7 and the burner bowl 5 are conducted to the burner cap supporting and heat transferring rod 28 that is installed to the upper portion of the fuel tank 4 to fix the burner cap 7 and the burner bowl 5. In addition, since a plurality of heat sinks 29 are installed to the lower end of the burner cap supporting and heat transferring rod 28, protruded into the upper surface of the fuel tank 4, the heat conducted through the burner cap supporting and heat transferring rod 28 is transferred to the heat sinks 29. [67] The heat conducted to the heat sinks 29 heats the inside of the fuel tank 4 so that the internal gas is expanded, thereby increasing internal pressure of the fuel tank 4. Thus, the increase of internal pressure makes the fuel be injected through the nozzle 9 more easily, and the fuel is then supplied through the guide tube 11. Thus, there is no need to pressure the inside of the fuel tank 4 frequently during the heating process. That is to s ay, owing to such configuration and operation, combustion heat is always conducted to the inside of the fuel tank 4 to increase pressure of the inside. In addition, since at least one heat sinks 29 is installed at regular intervals, the radiation area is increased and a pressuring force is enhanced. [68] In the preferred embodiment of the present invention, the combustion heat heats the heat sinks 29 installed in the fuel tank 4 so as to expand the internal gas of the fuel tank 4. Thus, fuel may be supplied to the nozzle 9 more easily, and there is no need of conducting a separate pressuring action after ignition, which allows the portable stove to be used very conveniently. [69] In addition, in the stove according to the preferred embodiment of the present invention, the fuel injection hole 2 is formed so that a gas discharge hole 2a is formed at a position below a side of the fuel injection hole 2. Thus, when the fuel cap 1 is dissembled from the fuel injection hole 2 after the stove is used, a high temperature gas in the fuel tank 4 is discharged downward toward the ground, thereby protecting users. [70] In the drawings, reference numerals 17 and 18 denote ventilation holes for assisting in combustion of fuel. [71] Now, methods for using and operating the portable multi-fuel stove according to the preferred embodiment of the present invention are described as follows. [72] First, in case of using the stove of the present invention as a gas stove using butane, a connector 21 connected to a butane valve 24 and a hose 22 combined to a butane container 25 is combined to the fuel cap 1 in which the gas injection hole Ia, the check valve Ib and the safety valve Ic are installed. Then, the butane valve 24 is opened, and the stove 100 is ignited for use. At this time, butane gas injected into the fuel tank 4 is continuously supplied to the nozzle 9 of the flame control valve 10 through gas tube 13 inserted into the dual preheating tube 8, and then combusted. [73] In this case, if gasoline is remained in the fuel tank 4, the gasoline and the butane are supplied to the nozzle 9 together and then combusted. That is, gasoline and butane may be used at the same time. [74] Here, installation positions of the gas injection hole Ia, the check valve Ib and the safety valve Ic are selected suitably on the upper portion of the fuel tank 4, not limitedly. However, it is more preferable that they are installed in the fuel cap 1 so that they may be more easily repaired, exchanged and combined to the connector 21. [75] Meanwhile, in case of using the stove of the present invention as a gasoline stove, a user combines the connector 21 connected to the butane valve 24 and the hose 22 combined to the butane container 25 with the fuel cap 1. Then, the user opens the butane valve 24 so that butane gas is injected into the fuel tank 4 through the gas injection hole Ia, the check valve Ib and the safety valve Ic installed in the fuel cap 1. [76] At this time, since butane is in a liquid state in the butane container 25, butane compressed in the butane container 25 is introduced into the fuel tank 4 just by opening the butane valve 24. The introduced butane presses gasoline in the fuel tank 4. Thus, the gasoline in the fuel tank 4 may be easily vaporized and injected at the nozzle 9 of the flame control valve 10 through the dual preheating tube 8, thereby ensuring easy ignition. [77] In addition, once butane gas is sufficiently injected into the fuel tank 4, the stove 100 keeps ignition and combustion though the connector 21 is separated from the fuel cap 1. [78] If the stove 100 is ignited after butane gas is sufficiently injected into the fuel tank 4, the butane gas filled in the fuel tank 4 is ejected and combusted through the nozzle 9 of the flame control valve 10 through the gas tube 13 installed in the dual preheating tube 8 at an initial stage, prior to the gasoline. In the butane combustion process, the dual preheating tube 8 and the flame control valve 10 are sufficiently preheated. Thus, when the gasoline inhaled by the inhaling member 14 and supplied to the flame control valve 10 through the dual preheating tube 8 is combusted just after the butane filled in the fuel tank 4 is completely combusted, the gasoline is sufficiently vaporized to ensure complete combustion. Thus, the phenomenon that red flame and black dirt are generated due to incomplete combustion of gasoline during a certain time for an initial ignition in a conventional gasoline stove does not happen in the present invention. [79] If the stove 100 is ignited, the dual preheating tube 8 is heated due to combustion flame. If the dual preheating tube 8 is heated as mentioned above, the gasoline passing through the dual preheating tube 8 is preheated to promote vaporization of the gasoline. In addition, the heat of combustion flame is conducted and convected by means of the gas tube 13 installed in the preheating tube 8 and gas (or, a mixed gas of air and gasoline vapor) filled in the gas tube 13. Accordingly, the gas (or, a mixed gas of air and gasoline vapor) in the fuel tank 4 is also heated to increase its kinetic energy and a vapor pressure of the gasoline in the fuel tank 4. Thus, though the gasoline is consumed due to combustion and thus the gas in the fuel tank 4 is partially flowed out through the dual preheating tube 8 and the gas tube 13, pressure may be applied suf¬ ficiently for vaporization and combustion at the nozzle 9. [80] Thus, combustion may keep on without any separate work for pressuring the gasoline in the fuel tank 4 like pumping, after ignition. [81] Meanwhile, if butane cannot be used as a pressuring means any more since butane is not prepared or the prepared butane is all consumed, a rubber hand blower 23 and a hose 22' may be used as an emergency pressuring means as shown in Fig. 10 in order to blowing atmosphere into the fuel tank 4. Even in this case, after ignition, fuel may be continuously combusted according to operation of the gas tube and its internal gas without any separating pressuring work like pumping. However, rock wool 27 is filled in the inner bottom of the burner bowl 5, and a common preheating process for inhaling and igniting gasoline in the rock wool 27 should be conducted. [82] Fig. 11 is a sectional view showing that the stove according to one embodiment of the present invention is received in a case 26. As shown in Fig. 11, the case 26 may have a body and a cover in order to receive the portable multi-fuel stove 100 of the present invention and also store a tripod 3. The body and the cover of the case 26 may be made to have kocher and fryer shapes and their surfaces may be treated in a suitable way so that the body and the cover may be used instead of a kocher and a fryer. It may reduce weight of burdens for outdoor leisure activities. [83] Though the present invention is described based on the embodiments with reference to the accompanying drawings, they are proposed for illustration only, and it should be understood that various changes, modifications and equivalents are possible to those skilled in the art. Industrial Applicability [84] As described above, the stove of the present invention may use gasoline and butane together. In particular, butane gas is injected into the fuel tank in a region above gasoline so that the butane gas is combusted at an initial ignition stage, thereby eliminating the need of preheating that results from incomplete combustion of gasoline at an initial ignition stage in a conventional gasoline stove. In addition, once a certain amount of butane is combusted, though butane is not supplied, gasoline is continuously inhaled, vaporized and injected by means of vapor pressure in an upper portion of the fuel tank and osmotic pressure of the inhaling member without any pressuring work for the gasoline. In addition, the present invention ensures the nozzle to be not easily separated but easily exchanged. Moreover, the gas discharge hole is formed downward at one side of the fuel injection hole, and the inhaling member is filled to a middle portion of the entire length of the preheating tube, so that the portable multi-fuel stove may have small and light structure.