ENVIRONMENT MONITORING SYSTEM

In an environment monitoring system using an optical flow, an optical-flow detecting device detects the optical flow in the steps of reverse-projection converting the early image of two early and later images picked up by an image picked up, on the basis of a predetermined optical arrangement of the image pick-up means onto an x-z plane in parallel to a road surface in a real space to acquire a road surface image; computing a moving distance of one's own vehicle in two timings on the basis of a time interval between two timings and speed information of one's own vehicle; parallel-shifting the road surface image by the moving distance thus computed; projection-converting the road surface image after parallel-shifted to acquire an estimated image of the later image in timing; acquiring a differential image between the later image and its estimated image to extract a feature point; and searching a corresponding point of the feature point extracted. In this configuration, it is possible to prevent an object such as a paint which should not be detected on a road surface from being erroneously detected as another surrounding vehicle.