PURPOSE: To omit the labor and the time required for designation of an ID and to eliminate the misrecognition of a closed area due to a mistake by recognizing automatically the closed area based on the geometric information on both start and end points of a boundary.

CONSTITUTION: A start boundary selection part 102 selects successively the boundary candidates out of a boundary data storage part 101, and a next boundary selection part 104 of a start/end point direction closed area recognizing mechanism 103 selects successively the other boundaries continuous toward the end point from the start point of a selected boundary in a counterclockwise- priority way. These selected boundaries are stored in a tentative closed area data storage part 109 via a boundary data output part 105. In the same way, a next boundary selection part 107 of an end/start point direction closed area recognizing mechanism 106 selects successively other boundaries. A boundary data output part 108 stores these selected boundaries in a tentative closed area data storage part 109. Then a counterclockwise checking part 110 checks whether a closed area consisting of the boundary data is formed counterclockwise or not. If so, the boundary data is stored in a closed area data storage part 111. Thus the closed area can be automatically recognized.