PURPOSE: To facilitate control of main steam temperature and reheated steam temperature while enhancing control response by heating the heater section and the reheater section of a pressure fluidized bed boiler with a pressure fluidized bed without restraining each other.

CONSTITUTION: Saturated steam an a steam drum 2 is superheated at the primary superheating section 8 of a superheating section pressure fluidized bed and heated further at a secondary heating section 10 before being supplied through a main steam pipe 11 to a steam turbine. Fuel supply to an evaporating section pressure fluidized bed 5 and the superheating sections 8, 10 is regulated, respectively, through fuel regulation valves 23, 25. Main steam temperature is controlled by regulating a spray water regulation valve 26 based on a signal from a main steam temperature detector 24. Low temperature reheated steam extracted from a turbine is then reheated at a reheating section pressure fluidized bed primary reheating section 14 and secondary reheating section 16 before being supplied to the turbine. Fuel supply to the reheating section is regulated through a fuel regulation valve 28. Temperature of reheated steam is controlled by a reheating section spray water regulation valve 29.