PURPOSE: To prevent the exhaustion up of a battery by installing a series circuit consisting of an ignition switch, the third resistance, and a diode between the nonharness side of one connector and a battery terminal, as for a switch circuit for vehicle which is connected with the power line having the voltage lower than the battery voltage.

CONSTITUTION: When an ignition switch is turned ON, electricity is supplied to the connectors 20A and 20B through the ignition switch 10, and the insulation film formed at the electric contact point between the connectors 20A and 20B is destroyed. Further, since, at this time, the voltage of a battery 9 is set higher than the voltage VDD of an electric power line, the insulation film can be destroyed by the electric current which is relatively larger than the conventional value, and the effect can be improved.