PURPOSE: To inform a driver of the dangerousness of a rear-end collision against a forward vehicle without trouble for measuring a car-to-car distance with the forward vehicle.

CONSTITUTION: Since a mark displaying a reference stopping position of a vehicle 1, namely, a reference stopping position display mark is constituted so as to be displayed the larger in speed, the higher in position at the upper side of a combiner C, when it is seen from a driver P of the vehicle 1, the mark comes to be displayed the faster in speed of the vehicle 1, the remoter on a road surface of the reference stopping position display mark in consequence. Accordingly, the driver P can drive the vehicle 1 in using the reference stopping position display mark being displayed in pile on the road surface as a criterion of a position where the vehicle 1 is stopped when an emergency brake is operated.