PURPOSE: To adequately control lighting inside a tunnel and establish a driving security by starting time metering when an automatic light adjusting device generates a lighting command signal, stopping the flime metering when a lighting apparatus comes on and outputting a failure detecting signal after a prescribed lapse of time.

CONSTITUTION: A timer. 51 starts its time metering when any one of contacts 9 to 15 of an automatic light adjusting device 1 is turned into ON state and a lighting command signal is issued. Normally closed contacts 41b to, 47b of auxiliary relays 41 to 47 are operated in linkage make and break of normally open contacts 2a to 8a of a contactor. In case that anyone the cntacts 9 to 15 of the automatic light adjusting device 1 issue the lighting comnand signal, time metering is stopped when the corresponding contactor is made, and the time metering is continued when the contactor is not made. And, a contact 51a is turned into ON state when the timer 51 meters a stated time so as to turn the normally open contact 52a of a failure detecting auxiliary relay 52 into ON state for outputting the failure detecting signal. Thus, the lighting inside a tunnel can be adequately controlled and the security for drivers can be established.