A turbine generating apparatus includes a control unit which controls the turbine generating apparatus as follows. During a system connection running mode, a fuel is fed to the gas turbine at a fuel flow rate corresponding to a preset load. The converter prepares a pseudo-system in which a frequency conforms to a set rotational speed of the gas turbine at the preset load, and converts an output of the generator to a direct current in a state that a number of revolutions of the gas turbine is specified by operating the generator synchronously with the pseudo-system. A power to be taken out is controlled depending on a magnitude of a turbine output. The inverter converts a DC voltage output from the converter to an AC voltage by a pulse width modulation at a system voltage and a system frequency so as to keep the DC voltage output from the converter at a predetermined voltage.