PURPOSE: To prevent rear-end collision at the time of deceleration control by energizing a danger information signal if present deceleration calculated from vehicle speed detected by a speed detecting means is less than a threshold value.

CONSTITUTION: A controller 5 computes present deceleration from vehicle speed obtained by a vehicle speed detecting means 2. If this value is smaller than specified deceleration (threshold value) obtained from an experiment or the like, a hazard lamp serving as a danger information means 8 is blinked automatically to notify a subsequent vehicle that there is a danger of rear-end collision because of tool large deceleration of the own vehicle. It is thus possible to prevent rear-end collision by the subsequent vehicle at the time of deceleration control.