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 (IGV) 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 (IGV) 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. <EOS>