First FET switches control supply of electricity from an external power supply to a primary winding of a transformer. A condenser is connected, in series, to a secondary winding of the transformer. A second FET switch is connected, in parallel, to the secondary winding and the condenser. The diode is connected, in parallel, to the second FET switch. A switch control unit acquires a value obtained by measuring a current flowing through the first FET switches and the second FET switch and controls, on the basis of the measurement result of the current, conduction of the first FET switches and the second FET switch.