SCANNER Technical Field [1] The present invention relates, in general, to a scanner and, more particularly, to a scanner, capable of scanning general paper as well as identification cards, such as a resident registration card or a driver's license. Background Art [2] Generally, the following methods have been widely used to input data into a computer. When a person carries out word processing or CAD work using a keyboard or a mouse, the processed data are thereby input into a computer. Alternatively, contents or pictures of books or documents are directly read, and thereafter the read data are input into a computer. As such, the method of directly reading the contents or pictures of books or documents and inputting the read data into a computer is realized by a scanner. That is, the scanner is a device which converts sensed images into an image data file, after sensing images printed on paper. The general scanner is operated as follows. That is, a sheet of paper to be scanned is fed into the scanner, and light beams irradiate the paper. Due to reflected light, images printed on the paper are recognized. The recognized images are converted into digital data, prior to being stored in a storage means of a computer or a memory of the scanner. [3] The scanning methods of the scanner are typically classified into a sheet-fed method and a flat bed method. The sheet-fed method is usually used in facsimiles. That is, the scanner adopting the sheet fed method scans image data line by line while feeding a page. Unlike the sheet fed method, the flat bed method is usually used in copying machines. That is, the scanner adopting the flat bed method moves across a stationary page, thus scanning image data. [4] Meanwhile, when one desires to scan an identification card, an additional small scanner different from a general scanner must be used. Thus, two scanners are required to scan both general paper and identification cards, so that a heavy burden of expense is incurred and a large installation space is required, thereby it is difficult to satisfy consumers' demands. Disclosure of Invention Technical Problem [5] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a scanner, capable of scanning both normal-sized paper and identification cards using one scanner. Technical Solution [6] In order to accomplish the object, the present invention provides a scanner, including a main body having an upper part and a lower part spaced apart from the upper part by a predetermined distance; a paper loading part provided on the upper part of the main body, with paper to be scanned being loaded onto the paper loading part; a support unit installed between the upper and lower parts of the main body, and holding an identification card to be scanned; a guide part to selectively guide the paper loaded onto the paper loading part or the identification card supported by the support unit; and a catch tray to hold the scanned paper or identification card which is guided by the guide part and thereafter discharged to an outside. [7] Preferably, the support unit includes a base mounted to a rear portion of the main body; a pair of guides provided on the base and spaced apart from each other by a pre¬ determined distance, with an insertion opening being formed between the guides; and a cover to cover a lower portion of the base. More preferably, the guides are movable in a lateral direction, according to a size of the identification card held by the support unit. It is most preferable that the scanner further include a circuit installed at a motor drive unit and delaying a scanning operation for a predetermined period so as to prepare for the scanning operation, according to the size of the identification card to be scanned, and an optical sensor installed between the upper and lower parts of the main body and spaced apart from the guides by a predetermined distance, and sensing the identification card to be scanned in a non-contact manner. Advantageous Effects [8] As described above, the present invention is capable of scanning identification cards as well as general paper using one scanner, thus satisfying consumers in terms of cost and space utilization. Brief Description of the Drawings [9] FlG. 1 is a perspective view showing a scanner, according to an embodiment of this invention; [10] FlG. 2 is a rear view of the scanner shown in FlG. 1 ; [11] FlG. 3 is a view showing a support unit mounted to the scanner of FIGS. 1 and 2; [12] FlG. 4 is an enlarged plan view showing the support unit of FlG. 2; and [13] FlG. 5 is an exploded view of the support unit shown in FlG. 2. Best Mode for Carrying Out the Invention [14] Hereinafter, a scanner according to the preferred embodiment of this invention will be described in detail with reference to the accompanying drawings. FlG. 1 is a perspective view showing a scanner, according to an embodiment of this invention. FlG. 2 is a rear view of the scanner shown in FlG. 1. [15] The scanner according to an embodiment of this invention includes a main body 102, a paper loading part 104, a support unit 106, a guide part 108, and a catch tray 110. [16] The main body 102 includes an upper part 103, and a lower part 105 which is spaced apart from the upper part 103 by a predetermined distance. The paper loading part 104 is provided on the upper part 103 of the main body 102, so that paper to be scanned is loaded onto the paper loading part 104. [17] The support unit 106 is installed between the upper and lower parts 103 and 105 of the main body 102, and holds an identification card to be scanned. FlG. 3 is a view showing the support unit 106 mounted to the scanner of FIGS. 1 and 2. FlG. 4 is an enlarged plan view showing the support unit 106 of FlG. 2. FlG. 5 is an exploded view of the support unit 106 shown in FlG. 2. The support unit 106 includes a base 402, a pair of guides 404, and a cover 406. The base 402 is mounted to a rear portion of the main body 102. The guides 404 are provided on the base 402, and are spaced apart from each other by a predetermined distance, with an insertion opening 109 formed between the guides 404. The cover 406 serves to cover the lower portion of the base 402. Meanwhile, the guides 404 function to support the identification card so that is does not deviate from a predetermined course, when the identification card is fed into the scanner by the operation of a roller. Preferably, a pair of guides 404 is movable in a lateral direction, so that the distance between the guides 404 may be adjusted, according to the size of the identification card to be scanned. [18] The guide part 108 functions to guide the paper loaded on the paper loading part 104, and the identification card held by the support unit 106. The catch tray 110 holds the scanned paper or identification card that has been guided by the guide part 108 and then discharged to the outside. [19] According to an embodiment of this invention, the scanner further includes a circuit (not shown) and an optical sensor (not shown). The circuit is installed at a motor drive unit (not shown), and delays the scanning operation for a predetermined period so as to prepare for the scanning operation according to the size of an iden¬ tification card to be scanned. Further, the optical sensor is installed between the upper and lower parts 103 and 105 of the main body 102 and is spaced apart from the guides 404 by a predetermined distance, and senses the identification card to be scanned, in a non-contact manner. [20] The scanner according to this invention constructed as described above is operated as follows. [21] An identification card, such as a resident registration card or a driver's license, is inserted into the insertion opening 109 which is formed between the pair of guides 404. Meanwhile, normal-sized paper, such as a document, is loaded onto the paper loading part 104. Next, when sensing a preparation for scanning, that is, an object to be scanned, the roller 302 of the scanner is actuated to move the object to a predetermined position. Thereafter, a scanning option is selected, and the object is scanned according to a scanning program. At this time, a user may confirm the scanned image. Pa rticularly, the data scanning identification cards are help to prevent illegal acts using false identity, and are useful in emergencies. Further, when it is required to identify someone, the scanner of this invention allows the person to be easily identified. When the scanner of this invention is used in a financial institution, the scanner stores data when a person first subscribes, thus allowing the person's identity to be rapidly determined. Thereby, it is unnecessary to copy and store an identification card, thus being convenient for the financial institution. Further, when this invention is used in a hotel, it is impossible for a person to assume a false identity when the person checks into the hotel. Furthermore, this invention affords easy confirmation of identification cards, thus preventing juveniles from entering merrymaking places or corruptive places, therefore protecting the juveniles from deleterious environments. [22] Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.