PURPOSE: To reduce power loss by providing the feeder line for a load with a switch circuit being turned OFF immediately upon detection of an overcurrent flowing through the feeder line to interrupt the overcurrent.

CONSTITUTION: Power is fed from a power supply 2 through a feeder line 3, a switch circuit 4 and a current detecting section 5 to a load 6. Current flowing on the feeder line 3 is detected at the current detecting section 5 in the form of a voltage value and delivered to a control section 1. When the input current value is higher than a set current value and sustains for a set time or longer, a decision is made that an overcurrent is flowing on the feeder line and a switch control section 11 is fed with a command for turning a switch OFF. Since an overcurrent is detected quickly and the feeder line 3 is interrupted accurately with high speed, power is not wasted and the service life of a battery, being used as a power supply 2, can be prolonged.