To enable operations with fuel gas pressure in both a case in which the fuel gas pressure is higher than a pressure optimum to the burner of a gas turbine and a case in which it is lower than that.

When a fuel gas pressure is lower than a pressure optimum to operation of the gas turbine, fuel gas is compressed by a fuel gas compressor and pressurized to an optimum pressure. Fuel gas compressed during starting is cooled by a cooler, a temperature is regulated to an optimum value, and fuel gas is fed to the burner through a heater bypass line. During normal operation, cooling by a cooler is not effected and the fuel gas is heated to an optimum temperature by a heater. Meanwhile, when a pressure of fuel gas flowing in from a fuel gas feed source is higher than a pressure optimum to operation of the gas turbine, the fuel gas is caused to bypass a fuel gas compressor and decreased in a pressure by a pressure reducing valve, and heated to temperature optimum to operation of the gas turbine and fed to the burner.