Abstract: A drawing is read by a scanner to create raster data. A labeling process is executed for the data to extract a contour line for each pattern element resultant from the labeling process to produce contour line data and region data to manage, in a tree structure, information related to a circumscribed rectangle of each line segment of the contour line. When the operator picks by a pointing device a predetermined region on the screen of a display and a pair of line segments for recognition, there is retrieved region data corresponding to the specified region. After extracting contour line data associated with the retrieved region data, a center line creation process is executed according to the extracted contour line data.