Generator apparatus

A generator apparatus such as in a cogeneration system has a controlling power supply energized with its generator output with giving no adverse effect on the waveform of its output. An inverter (13) is provided for converting an alternating current output of the engine generator (10) into a direct current and returning back by the action of its inverter circuit (133) to an alternating current of a predetermined frequency which is then connected to a power supply system (14). While the engine (11) remains not actuated, a power received from a joint between the inverter (13) and the power supply system (14) is rectified by a rectifier (141) and transferred to the controlling power supply (140). When the engine (11) is started, the power at the input of the inverter circuit (133) is transmitted to the controlling power supply (140). As the voltage at the input of the inverter circuit (133) is set higher than that at the power supply system side, the energization of the controlling power supply (140) with the power at the input of the inverter circuit (133) can automatically be selected after the start-up of the engine (11).