Duties of control for DC/AC and DC/DC conversion units are determined by considering electric influences of a filter circuit, a capacitor connected to a DC bus, and a DC reactor for an output voltage command value for supplying an AC voltage to a load. The DC/DC conversion unit is controlled to convert a DC voltage into a DC bus voltage waveform alternately having a period of a pulsating current waveform corresponding to the absolute value of the AC voltage and a period of the DC voltage as a pulsating current minimum value. The DC/AC conversion unit is controlled to perform step-down operation during the period of the DC voltage and thus perform conversion into a waveform of the absolute value of the AC voltage corresponding to the period of the DC voltage, and also to perform polarity inversion per one pulsating current cycle.