JPH05238367

PURPOSE:To prevent occurrence of billiard clash by providing a deciding means to decide a possibility of a preceding car colliding with a second car ahead of a self-car and a risk preventing means to perform risk preventing operation so that a self-car is prevented from collision with a preceding car when the possibility of collision is decided by the deciding means. CONSTITUTION:At S6, when it is decided that a second car ahead of a self-car is involved in collision, advance to S7 is effected, and an intercar distance L1B between a second car ahead of a self-car and a self-car, an automatic brake starting threshold L0B and an alarm generating threshold L2B are calculated. In which case, the intercar distance L1B between the second car ahead of a self-car and a self-car is calculated from an intercar distance L1 between a self-car and a preceding car and an intercar distance L1A between the second car ahead of a self car and a preceding car. The automatic brake starting threshold L0B is an intercar distance between the second car ahead of a self car and a self-car at which there is the possibility of the second car ahead of a self car making contact with a self-car and automatic brake is started to prevent the occurrence of a contact therebetween and calculated based on a current car speed V0 of a self-car. Further at an alarm generating threshold L2B, an alarm is sounded prior to the start of automatic brake.