To provide one means for reducing accidents in an over-all present road war.

A heavy automobile is conventionally and legally required to incorporate and mount a warning device. For a general automobile or the like other than the heavy automobile, a warning device at the back, right, or left turning time can be easily manufactured as an accessory set which its user purchases in an auto parts store in a town and can be easily mounted. Extreme increase of the number of possessed automobiles increases the road traffic jam and the confusion status every day, and the accidents are apt to increase. One of large causes of the accidents is that a vehicle collides against a following vehicle or a reversely running vehicle or hits a walking person when it turns right or left or move backward. A fact that only about 1 or 2% of heavy automobiles of all present automobiles have the warning device also causes the accidents.