To restrain combustion ash from depositing on a combustion floor, without stopping a combustor.

An ash flying pipe 38 connected to an air compressor 48 and a nozzle 40 turning in the combustion floor 16 direction, are arranged in a refractory wall 19. The combustion ash depositing on the combustion floor 16 is intermittently blown off by high pressure air coming out of the air compressor 48, and is discharged outside a combustion chamber 2 by being accompanied by combustion exhaust gas. As a result of it, a quantity of combustion ash depositing on the combustion floor 16 can be reduced, and combustion failure of a woody pellet can be prevented.