PURPOSE: To start up a synchronous capacitor without letting a large current flow by changing over the output frequency from low frequency to the frequency of a bus in order, and providing a breaker between an conversion output terminal and the bus, and opening it during the start-up of the synchronous capacitor, and closing it after completion of the start-up.

CONSTITUTION: The generation output of a shaft generator 2 is rectified during the start-up of a synchronous capacitor 17, and after this the output frequency is changed over in order from low frequency to the AC frequency of a bus 9, and a breaker 16 is opened during the start-up of the synchronous capacitor 17, and is closed after completion of start up. Hereby, it follows that the synchronous capacitor 17 is used as a synchronizer, and the induction motor for starting the synchronizer 17 becomes needless. Furthermore, the synchronizer 17 can be started up by a little starting current.