To confirm safety at the time of changing a traffic lane by taking a condition of a road in a wide range into consideration.

A condition of a road such as a reduction of traffic lanes in number, a profile of a road, the slope of a road, a presence or an absence of traffic accidents, and a condition of a road under construction, is confirmed by a road information extracting device 6 such as a navigation system, a road- to-vehicle communication system, a vehicle-to-vehicle communication system and the like. When it is detected by a winker operation detecting device 7 that a driver is trying to change a traffic lane with a winker operated, a load condition is confirmed so as to allow safety for changing a traffic lane to be automatically judged by a traffic lane change right or wrong judgement processing part 8, and when a case is judged as danger, the driven is informed of it by an informing device 9 of a fact that change in traffic lane is dangerous.