To indicate the change of a lane and the movement of a vehicle by detecting the approach of a bus to the vehicle.

A bus/automobile relative position analyzing part 13 receives a signal showing the position/lane of a bus which is running, detects the position/lane of an automobile, and performs analysis based on the positions/lanes of the bus and the automobile to see whether either the bus or automobile has traveled on the same lane as the other and approached the other relatively. If the bus and the automobile have approached each other on the same lane, a bus approach reporting part 18 either displays it on a display device 16 or issues a voice alarm from an audio device 17.