A drive circuit is provided with an input terminal for receiving input signals, an output terminal that outputs drive signals generated from the input signals, a control power supply terminal that receives a control power supply voltage, an output terminal that outputs an output signal, and a reset terminal that receives a reset signal. The output signal is given to a gate of a MOSFET. A secondary side circuit and a MOSFET constitute a step-down chopper circuit, which steps down a voltage through duty ratio control of the gate drive signal and generates a control power supply voltage. Upon receipt of a reset signal, the drive circuit stops outputting the drive signal and changes the output signal so as to reduce the control power supply voltage VCC.