PURPOSE:To control ignition and the combustion condition of a combustible material charged in a furnace and to normally obtain the constant quantity of heat, by controlling the energizing order of air feed pipes. CONSTITUTION:A space 19 is provided between an enclosed casing 14, a furnace 16 and a cyclone device 18, and is filled with water through an introducing port 20. Thereafter, a combustible material is charged in a first combustion chamber 40 through a combustion material charge inlet 46. The air, introduced to the ignited combustible material positioned at the upper part with the aid of a blower 72, is discharged in a furnace 16 from a blast plate 56 through an air pipe 30. From the viewpoint of the nature of the laminated combustible material, penetration of the air is not expectable too much, whereby an electromagnetic valve 118 is opened following energization of a blower 106, the fed air flows to an air feed unit 92, is branched by passages 98, 100 and 102, and is injected in a furnace 16 through a nozzle part 104. Finally, with the aid of the air from the air feed unit 92, a combustible material is burnt without being influenced by any obstacle factor.