To control a temperature of a fluidized bed without using any auxiliary fuel and to restrict occurrence of polluted gas at a fluidized bed type combustion (ignition) device.

Air 17 supplied to a fluidized bed 18 is heated by combustion discharged gas at an air preheater 12 and concurrently a temperature of the fluidized bed 18 is detected by a sensor 19, and an amount of cooling medium 21 atomized at 13 against the combustion discharging gas is controlled in reference to the detected value. With such an arrangement as above, a temperature of air fed to the fluidized bed 18 is also controlled.