PURPOSE: To make possible the exact measurement of a road curve on this side thereof by estimating the condition of an advance road of a running car from an image of a forward visual field.

CONSTITUTION: A rear-end collision device mounted on a running car is provided with a distance measuring device 1, an image input device 6, an image processor 7, an information processor 2 and an alarm 3. A distance between a forward car and a rearward car is measured by the use of the distance measuring device 1 and with the use of the image input device 6 a forward visual field is photographed to produce an image. Within the image processor 7 the image is processed to detect a white line and the like on a road and a forward road curve of an advance road is estimated. Within a measurement area setter 8 of the information processor 2 the measurement area of the distance measuring device l is set in response to said estimation result. Within an information judging device 9 the possibility of rear-end collision against the forward car is judged from the measurement result by the use of the distance measuring device 1 and the alarm 3 is operated on the basis of the discrimination.