In this paper we described a new technique for measuring a distance to the front vehicle using stereo images. Only vehicles traveling in the driver's lane need to be detected. Thus the driver's lane is determined as the processing region in the images. Usually detecting lane markers does this. However, when the front vehicle appears in the near sight, it is not necessary to detect lane markers to the far sight. On the other side, when the front vehicle appears in the far sight, it is necessary to detect lane markers to the far sight. So we adopt the hierarchy process to detect the front vehicle.