PURPOSE: To assure the discharge of ashes, by providing a feeder screw for an air charge pipe of a combustion chamber to prevent clogging of air charge holes.

CONSTITUTION: A blower tube 12 is installed on top of rear wall 11 of a combus tion chamber 10 and a screw feeder for fuel 13 thereunder. An air charge pipe 16 has a number of air charge holes 17 and feeder screws 18. Solid fuel in a hopper 23 is transfered by the feeder 13, falls therefrom onto the feeding side 18' of the screw feeder 18, during which said solid fuel is ignited, and burnt to ashes before it reaches an ash chamber 19, falling therefrom through an ash discharge port 22. In such a manner, discharging of ashes is smoothly performed without producing clinkers; therefore, clogging of the air charge pipe 17 does not occur and the air charge pipe 16 is not buried in ashes.