To provide a compact and low-priced overcurrent detection device that can measure a load current and detect an overcurrent without a current sensor and a shunt resistance.

A drain-source voltage of a load drive FET 4 activating a load 3 is detected by an amplification circuit 5 and also a temperature of the FET 4 is measured by a temperature measuring circuit 8. Then, a current value flowing in the load 3 based upon the drain-source voltage and the temperature is calculated by a load current calculating means placed in a microcomputer 9 and an overcurrent is detected.