When it is determined that a type of a physical body in real space corresponding to an image portion is a crossing pedestrian, a distance calculating unit 13 performs a first distance calculating process of calculating a distance between a vehicle 1 and the physical body, on the basis of a correlative relationship between the distance from the vehicle 1 set on assumption of a height of the pedestrian and a height of the image portion, according to the height of the image portion. When it is determined that the type of the physical body is not the crossing pedestrian, then the distance calculating unit 13 performs a second distance calculating process which calculates the distance between the physical body and the vehicle, on the basis of a change in size of the image portions of the physical body extracted from time-series captured images.