To reduce the risk of receiving an electric shock at collision of a car, by generating collision detection information by a collision detector at the collision, and opening a switch by a switch controller, based on this information.

When a car is in a normal state of normal driving, a DC power source 1 generates a voltage V and supplies power to a load circuit 2. If the car collides, a collision detector 4 detects the collision, and transmits its being in a collided state to a switch controller 3 via a signal line 20. Based on this, the switch controller 3 opens switches 12-17, and cuts off the connection between both contacts of each switch. Consequently, voltages generated in the DC power source are about V/5 even at the highest, and can be lowered compared with the voltage V which is normally generated by the DC power source 1 at a normal operation time, and it becomes possible to reduce the risk of receiving an electric shock, regardless of the location of the breaking of wire caused by the collision.