PURPOSE: To detect a graphic to be a closed graphic without omission by stacking the branch point when endpoints are shared by plural segments.

CONSTITUTION: A start point is decided to be an endpoint 1, and a segment 102 sharing an end point 2 is detected. Moreover, the segment sharing an endpoint 3 at the opposed side is detected, and segments 103, 107, and 108 are present. Then, an angle between the segment 102 and the segments 103 and 107 is the largest, the segment 103 whose length is short is adopted, and the segment sharing an endpoint 4 is searched as a trace. At that time, the segments 107 and 108 are stacked. Thus, the trace reaches the segment 107 by continuing the trace. A branch is present also at the endpoint 3, a segment 108 is selected as a track segment, and the segments 102 and 103 are stacked. Thus, the trace reaches a segment 110 and the start point 1, and a closed graphic 200 can be outputted.