PURPOSE: To eliminate and correct the lowness in the response of the state of combustion of a solid fuel and make it possible to conduct a sensitive control on the state of combustion by controlling the condition of combustion by actuating and stopping mechanisms which include respective fuel supply mechanisms in three-stage temperature ranges and at the same time controlling in two stages the conditions of operation of a fuel supply mechanism.

CONSTITUTION: When a high temperature sensor 71 issues NO signal that indicates that in the inside of a combustion chamber 2 the temperature exceeds the high temperature limit, all of a class 6 of mechanisms stop at once or after they have completed their operation actions. And the fire of a solid fuel is extinguished. When a temperature setting sensor issues YES signal that indicates that in the inside of the combustion chamber 2 the temperature is below a set temperature, the control that is the same as with the operation switch being ON is restarted. And, on the contrary the high temperature sensor 71 issues YES signal that indicates that in the inside of the combustion chamber 2 the temperature is below the high temperature limit and the temperature setting sensor 72 issues NO signal that indicates that in the inside of the combustion chamber 2 the temperature is over the set temperature, the operation action of a fuel supply mechanism 62 is carried out for a short time and the rotation of the grate is not made and the combustion operation that keeps the solid fuel from being extinguished is made with a small fire burning.