To support the car driver and to increase the traffic safety, development of the driver assistance system is an important subject. Especially development of the driver assistance system which combines an in-vehicle camera with image processing technology is an interesting subject. In this paper we described a basic technology for the driver assistance system using in-vehicle camera, which detects the car ahead in the in-vehicle camera image. This paper presents following two algorithms. （1） Algorithm to generate search area for the car ahead, based on a virtual running space. （2） Algorithm to detect car ahead according to the density of horizontal edges in the image, and symmetry of vertical edges.