PURPOSE: To permit the self sustaining of a gas turbine in the low load operation, in order to spread the operation load region by permitting the partial load operation, in a pressurizing fluidized bed combined plant equipped with a single axis type gas turbine equipment.

CONSTITUTION: If, in the low load operation, a gas turbine 2 can not sufficiently drive an air compressor 1 by only the combustion gas 23, and the sufficient compressed air cannot be supplied into a pressurized fluidized bed boiler 4, the supplied steam to a high pressure turbine 5, exhaust steam, reheated steam, and high pressure supplied-water to a high pressure turbine, and the steam supplied from other steam generation, etc., are supplied into the gas turbine 2, and the driving energy for the gas turbine is supplemented by the energy of the supplied steam, etc., and the power for an air compressor 1 is secured.