PURPOSE: To provide a self-diagnosis circuit, which can automatically check the wire connecting state of an electric device.

CONSTITUTION: In an electric circuit, a load driving circuit and a switch 4 constituting an operating part are connected through a connector 2. In this electric circuit, a fuse 9 for checking the connection of the connector 2 is provided between a normally open contact point 4a and a movable contact piece 4c of the switch 4. A wire breaking circuit 8, which allows the fusing current flow into the fuse 9 based on the connector connecting signal outputted from a microcomputer 5, is provided at the halfway of a circuit for connecting the normally opened contact points 4a of the switch and the microcomputer 5 for controlling the load driving circuit. Since the connecting state of the connector 2 is automatically checked, it is not necessary to check the wire connecting state by manual work.