PURPOSE: To allow the complete combustion of solid fuel primarily comprising waste plastic, paper, lumber, etc., by providing a rooster rotating mechanism which rotates the grate on the horizontal plane, an ignition burner which ignites the solid fuel supplied by a fuel supply mechanism, and a secondly combustion burner which prevents black smoke from being produced.

CONSTITUTION: For catch fire, a motor 21 is first started to drive a fuel supply screw 3 to supply a proper amount of fuel for producing a pilot fire on the grate, and an ignition burner 17 and a secondary combustion burner 18 are operated. The ignition burner 17 causes the solid fuel to burn, and, after the flame temperature is detected to have risen to higher than 400°C, preferably higher than 600°C, the fuel supply screw 3 is started. Within one minute after the steady combustion is attained, fan 10 and fan 11 are started to supply the primary air and secondary air. Once the combustion of the solid fuel has stabilized, the secondary combustion burner 18 is extinguished.