We at Daihatsu Motor Co., Ltd., have been studying various technologies to measure distance values using image processing, especially binocular stereo, for Advanced Safety Vehicle (ASV) projects which ae suggested by the Ministry of Transportation. A problem concerning the stem is a high computational cost. It is indispensable for a mass product application to implement a video rate processing by the minimum computational cost, therefore some improvements of stereo algorithms are needed. It is possible to extract optical flow with a low computational cost under some constraint condition in time varying images. In this paper we would like to report a video rate distance headway measurement method using stem image processing combined with optical flow.