This invention relates to a picture processing device in which picture data of a road or lines marking off a lane taken by a television camera installed on a vehicle is processed for the recognition of the contour of the road or the lane. Picture data is analog/digital converted, then edited and is subjected to the binary processing to be supplied to a digital differential analysis computing circuit. The digital differential analysis circuit comprises circuits serially connected each of which computes a rotary motion recurrence formula every rotation by a rotation angle. The recurrence formula is computed in the pipe-line system. In this computation the Hough transform is performed to give sine curves in a .rho.-.theta. coordinate system. The points of intersection of these sine curves (Hough curves) are given, and those of them having more occurrences are selected in the .rho.-.theta. coordinate system. Resultantly, the contour of the shoulder lines and the center line of the road, or the contour of the lane are given.