1. An edge detecting apparatus comprising: video camera means for generating an image of a road surface, said image including at least one boundary of said road surface; means for converting said image into image data comprising an array of image pixels; edge detecting means for detecting a position of an edge of said boundary of said road surface, said edge detecting means comprising a plurality of edge detecting masks, each of said edge detecting masks comprising an identical matrix of weighting coefficients, said edge detecting masks being imposed over said array of image pixels at differing angular orientations with respect to said array of image pixels, wherein the angular orientation of each edge detecting mask is shifted by a given angular interval from another said edge detecting mask, and calculating means for performing a sum-of-products operation between respective weighting coefficients in each edge detecting mask and a signal intensity of said image pixels located at corresponding positions of said respective weighting coefficients, and producing respective output values for each of said edge detecting masks; edge output selecting means for selecting an edge detecting mask exhibiting a maximum output value from among said edge detecting masks and selecting a predetermined number of edge detecting masks disposed before and behind the edge detecting mask exhibiting the maximum output value; and interpolating circuit means for estimating by interpolation a true direction of the edge on the basis of angles at which the respective edge detecting masks selected by said edge output selecting means are disposed with respect to said array of image pixels and by the output values of the selected respective edge detecting masks.