To effectively use cooler exhaust heat and improve gas turbine efficiency by applying the constitution that the cooling medium outlet pipe of a cooler to cool the air of a gas turbine easing introduced to a combustor as the atomizing air is connected to a heater laid in a pipeline for fuel fed to the combustor.

The casing air of a gas turbine casing air system 1 is made to flow to a combustor 4 via a cooler 2 and a compressor 3, and oil fuel flows in an oil fuel pipe 10 from a fuel tank 5 and is supplied to the combustor 4 via a fuel pump 6 and a fuel control valve 7. In this case, the cooling water outlet pipe 9a of the cooler 2 is connected to the inlet of a fuel heater 11 laid on the oil fuel pipe 10, and the outlet of the fuel heater 11 is connected to a cooling water pipe 9 leading to the inlet of the cooler 2. According to this construction, oil fuel is heated in the fuel heater 11, due to the exhaust heat of the cooling water of the cooler 2 after cooling the turbine casing air supplied to the combustor 4, and the exhaust heat of the cooling water is effectively used to improve gas turbine efficiency.