A first conversion circuit is electrically connected between a reference potential point and a first input point on a high potential side of a direct current power supply. A second conversion circuit is electrically connected between the reference potential point and a second input point on a low potential side of the direct current power supply. A voltage-regulating circuit is configured to adjust a magnitude of an applied voltage to the first conversion circuit and the second conversion circuit. The voltage-regulating circuit is configured to increase the magnitude of the applied voltage over time during a start time period from a start of supplying power from the direct current power supply until a first capacitor and a second capacitor are charged to a specified voltage.