PURPOSE: To prevent a failure of putting off an auxiliary light, by providing an interlocking controller to make the auxiliary light in the putting off condition linking to the OFF operation of a switch, when either the OFF operation of the ON/OFF switch of a headlight and a small light, or the OFF operation of an ignition key switch is operated.

CONSTITUTION: Even though a switch 11 is turned off in the condition of putting off a fog light 1, a relay switch 3 is OFF, and a current is not generated between the emitter and the corrector of the transistor TR6 of a light switch cancel circuit 12, so as to leave the transistor TR6 in the OFF condition, no one-shot pulse is output from a one-shot trigger generating circuit 7, and the fog light 1 is left as in the OFF condition. On the other hand, when an ignition key switch 4 is turned off in the condition of lighting the fog light 1, the fog light 1 is put off as well as the relay switch 3 is turned off.