The invention is directed to a method and apparatus for detecting a lane on a road, the latter of which includes an edge sensor (ED) for detecting edges indicative of boundaries of opposite sides of each lane, an edge memory (EM) for storing the edges to form a couple of continuous lines of edge groups indicative of the opposite boundaries of the lane, and an image processor (DP) for defining the opposite boundaries of the lane on a plane in a three-dimensional geometry. A center of curvature defining device (RC) defines a center of curvature to the opposite boundaries of the lane. An edge line extracting device (ES) divides the edge groups stored in the edge memory into a plurality of continuous regions each having a predetermined length along a concentric circle arc having the same center as the center of curvature, and extracts a pair of edge lines from each region. A tangent defining device (TL) defines a couple of tangents to the edge lines, and a normal defining device (NL) defines a normal to the tangents. Then, a segment setting device (SD) defines a couple of intersections of the normal with the tangents, and sets a line segment between the intersections as a segment of the lane. The image processor (DP) renews the opposite boundaries of the lane on the basis of the segment of the lane.