Power is generated from a wind turbine generating section (10). A phase control signal S3 is generated from a phase control signal generating section (16) in accordance with the power value of generated power (DC voltage). A synchronization control signal S2 is generated by a synchronizing section (15) based on the AC voltage E1 and frequency F1 on the system power supply side. Power supplied from the wind turbine generating section (10) is converted into a predetermined AC voltage E2 based on the phase control signal S3 and the synchronization control signal S2. The converted AC voltage E2 is supplied to a system power supply through a connecting section (13).
