A drive circuit is connected to a gate terminal of an FET connected to a DC power supply to be transformed and controlled to be turned on or off, and applies a voltage to the gate terminal to turn on the FET, the FET including a drain terminal to which a current is input, a source terminal that outputs the current input from the drain terminal, and the gate terminal that controls the current flowing from the drain terminal to the source terminal. A reverse bias circuit includes a capacitor connected to the source terminal of the FET, and a coil having one end connected between the drive circuit and the gate terminal and the other end connected between the capacitor and the source terminal.