An inverter circuit is connected in series to an AC power supply, and at the subsequent stage, a smoothing capacitor is connected via a converter circuit including semiconductor switching devices. A control circuit controls the converter circuit by providing a short-circuit period for bypassing the smoothing capacitor in each cycle, and controls the inverter circuit to improve the power factor of the AC power supply by using a current instruction such that the voltage of the smoothing capacitor becomes a target voltage. When the voltage of a DC voltage source of the inverter circuit has exceeded a predetermined upper limit, the control circuit increases the current instruction to control the inverter circuit, thereby increasing the discharge amount of the DC voltage source. Thus, even if the voltage variation of the DC voltage source of the inverter circuit increases, it is possible to stably continue the control.