1. A device for detecting a road traveling lane, from images on a road surface continuously picked up by image pickup means, comprising: edge point detection means for detecting a plurality of edge points in a contour on the image; edge histogram producing means for producing a vertical edge histogram for horizontal elements of the plurality of edge points detected by said edge point detection means; block marking line determination means for determining presence and absence of a block-like marking line on the basis of periodicity of distribution and a combination of distributions of plus edges and minus edges in the vertical edge histogram produced by said edge histogram producing means, and defining a region where said block-like marking line is present; lane boundary edge detection means for detecting vertical edge points present outside of a center of said traveling lane, in the region where said block-like marking line defined by said block marking line determination means is present; and lane boundary position defining means for defining a position of a curve fitted to the vertical edge points detected by said lane boundary edge detection means, as a position of a boundary of said traveling lane.