To stop the supply of power before an electric device is damaged or is defective in itself in the case of supplying power even when a cable for power supply is mis-connected or the like.

A microcomputer 8 is started when receiving a current from a power supply circuit 1, and controls a constant voltage circuit 2 so as not to apply a load voltage to a resistor R1. A DC current for load resistor sensing is supplied to a camera device 30 via a resistor R2 and a diode D1 and a comparator 3 supplies a level signal denoting a load resistor RL is a prescribed value or over to a port P1 of the microcomputer 8. When the level signal fed to the port P1 is at '1', that is, when the load resistor RL is at a prescribed value or over, the microcomputer 8 controls the constant voltage circuit 2 so as to supply the current to the camera device 30. When a fault current flows to the camera device 30, the microcomputer 8 controls the constant voltage circuit 2 so as to stop the supply of the current.