An extraction method of contour lines from a contour map on the market and their restoration method are described. Twin tracing points (clockwise and counterclockwise) are used to trace and extract line components from the map which involves not only contour lines but also block components such as symbols and numerals. To implement the tracing successfully, ending conditions and setting manners of the twin tracing points are dealt with taking various kinds of curves into consideration. By this method, sets of the coordinates of traced contour lines, step numbers of tracing, and moreover, the thickness and length of traced contour lines, the coordinates of their skeleton lines are obtained. Since some contour lines are cut off by the elimination of symbols and numerals, to restore them a finding method of a pair of cut off points which must be connected is also described. For the restoration, an adjacent graph is introduced with an example, and several cases of relations between a graph and set of contour lines are dealt with. A determining algorithm of a pair of connecting candidates is given. Finally, as the results, an original contour map of a mountainous area, extracted contour lines, skeleton contour lines and a connected (by straight lines) contour map obtained through the twin-tracing-points method and restoration method are illustrated.