To supply an electric power of improved quality to a load system by controlling a wind energy bus line voltage within a tolerable voltage range to suppress voltage fluctuation.

A detection voltage detected from a system bus line 1 is inputted in a voltage deviation preventing/controlling device 15. If the detection voltage deviates out of the tolerable voltage range, the detection voltage value is processed in addition or subtraction to control a capacitor 13 and a branch reactor 12 of a reactive power control circuit 10, so that a voltage of the system bus line 1 of wind energy in a reactive power compensator SVC is controlled to a prescribed value.