1. A device for detecting a road traveling lane, comprising: image pickup means for picking up images on a road surface continuously, edge point detection section for detecting a plurality of edge points in a contour on the image; edge histogram producing section for producing a vertical edge histogram for horizontal elements of the plurality of edge points detected by said edge point detection section; block marking line determination section 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 section, and defining a region where said block-like marking line is present; lane boundary edge detection section 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 section is present; and lane boundary position defining section means-for defining a position of a curve fitted to the vertical edge points detected by said lane boundary edge detection section, as a position of a boundary of said traveling lane; wherein said lane boundary edge detection section detects the edges of the lane boundary in an interval between neighboring block lines, on the basis of such a relationship that a vertical region between a peak of a plus edge histogram and a peak of a minus edge histogram corresponds to the interval between neighboring block lines, in said vertical edge histogram produced by said edge histogram producing section.