PURPOSE: To form the whole shape data of a workpiece in one time of operation by extracting the composite region of the whole workpiece with reference to the shape data of respective parts and the predetermined data composite require ment to compose the shape data of the respective parts in the composite region.

CONSTITUTION: While the shape of a workpiece is divided into a plurality of parts, the shape data of the respective divided parts are obtained to extract the composite region of the whole workpiece with reference to the shape data of respective parts and the predetermined data composite requirement and by a composite region extracting section 1. The shape data of the respective parts are composed in the composite region by a data composing and preparing section 9 to form the shape data of the whole workpiece. Thus, the shape data of the whole workpiece can be obtained in one time of operation without repeating a plurality of operations.