A twin-shaft gas turbine comprising: - a gas generator including a compressor configured to generate compressed air, - a burner configured to burn a fuel mixed with the compressed air received from the compressor to generate combustion gas, and - a high-pressure turbine configured to be rotationally driven by the combustion gas received from the burner and to generate driving force for the compressor; - an output turbine including a low-pressure turbine configured to be driven by exhaust gas received from the high-pressure turbine and a power generator configured to be driven by the low-pressure turbine; - an inlet guide vane for controlling the amount of air to be input from an atmosphere to the compressor; - a compressor extraction valve configured to release a portion of compressed air extracted from the compressor to the outside of the twin-shaft gas turbine; and - a control device configured to perform control of the rotational frequency of the gas generator and the output turbine, wherein the rotational frequency of the gas generator balanced with the low-pressure turbine with the power generator in the full-speed no-load operation (FSNL) state without the control device is referred to as a first rotational frequency, the control device is further configured to perform control: (i) to increase the rotational frequency of the gas generator in the full-speed no-load operation (FSNL) state from the first rotational frequency, and (ii) to get the rotational frequency of the gas generator in the full-speed no-load operation (FSNL) state when the power generator runs at 50 Hz higher than a resonance rotational frequency of the gas generator, with the low-pressure turbine balanced at rotational frequency of the low-pressure turbine in the full-speed no-load operation. - a gas generator including a compressor configured to generate compressed air, - a burner configured to burn a fuel mixed with the compressed air received from the compressor to generate combustion gas, and - a high-pressure turbine configured to be rotationally driven by the combustion gas received from the burner and to generate driving force for the compressor; - an output turbine including a low-pressure turbine configured to be driven by exhaust gas received from the high-pressure turbine and a power generator configured to be driven by the low-pressure turbine; - an inlet guide vane for controlling the amount of air to be input from an atmosphere to the compressor; - a compressor extraction valve configured to release a portion of compressed air extracted from the compressor to the outside of the twin-shaft gas turbine; and - a control device configured to perform control of the rotational frequency of the gas generator and the output turbine, (i) to increase the rotational frequency of the gas generator in the full-speed no-load operation (FSNL) state from the first rotational frequency, and (ii) to get the rotational frequency of the gas generator in the full-speed no-load operation (FSNL) state when the power generator runs at 50 Hz higher than a resonance rotational frequency of the gas generator, with the low-pressure turbine balanced at rotational frequency of the low-pressure turbine in the full-speed no-load operation.