A discharge switch and a capacitor are connected in series between first and second DC power supply lines. A boost circuit boosts a rectified voltage to charge the capacitor. An inverter receives the rectified voltage as a DC voltage when the discharge switch is not conducting, receives a voltage across the capacitor as the DC voltage when the discharge switch is conducting, converts the DC voltage into an AC voltage, and outputs it to a motor. A switch control unit maintains the discharge switch not conducting over a first time period, and switches the discharge switch between conducting and not conducting in a second time period. A charge and discharge time period setting unit sets the first time period when a rotational speed of the motor is higher than a speed threshold shorter than the first time period when the rotational speed is lower than the speed threshold.