An impedance adjustment circuit varies an impedance of a transistor, thereby adjusting an impedance of a current path. A second control circuit controls a drive circuit to turn on or off at least one switch device of the switch devices while the impedance adjustment circuit is increasing the impedance of the current path. The impedance adjustment circuit adjusts the impedance of the current path to the minimum value after the drive circuit switches the at least one switch device from off to on or from on to off.