A transformer that realizes ZVS operation includes a primary winding and a secondary winding. A control circuit turns switching elements on and off in a complimentary manner in order to repeatedly invert the voltage applied to the primary winding. A conduction path supplies a voltage excited in the secondary winding to a load connected between a high-potential side and a ground side of the secondary winding. A first rectifier diode has a rectification direction extending from the high-potential side toward the ground side of the load and is provided along the conduction path. A second rectifier diode and a capacitor, which are connected in series with each other, are connected in parallel with the secondary winding. An inductor is connected in parallel with the second rectifier diode. A rectification direction of the second rectifier diode matches the direction extending from the high-potential side to the ground side.