A conductor is placed on a first placement portion of a heat dissipation member with an insulation member interposed therebetween. An FET is electrically connected to the conductor. When current flows between the drain and the source of the FET, the FET generates heat. A second placement portion of a circuit board is placed on the conductor. The conductor and the insulation member are sandwiched between the first placement portion and the second placement portion. In the heat dissipation member, a first extension portion extends from the first placement portion, and in the circuit board, a second extension portion extends from the second placement portion. The first extension portion is located opposite to and is spaced apart from the second extension portion, and a microcomputer is placed on an upper surface of the second extension portion. The microcomputer outputs a control signal for turning the FET ON or OFF.