A controller 43 turns on a semiconductor switch 41 in a normal mode, and turns off the semiconductor switch 41 in a sleep mode. A bypass resistor 5 is connected in parallel to the semiconductor switch 41. A resistance value of the bypass resister 5 is so large as that in the sleep mode, a dark current is supplied to an electronic device 3 via the bypass resistor 5, and if an electric wire downstream of the bypass resistor is short-circuited, an electric current more than a permissive current is prevented from flowing to the electric wire.