Abstract: An object to be measured is measured with marks formed on a platen surface with the object to be measured mounted thereon. At least three or more marks are formed on the platen surface. The marks are formed so as to uniquely determine a combination of sizes of at least three marks arbitrarily selected and intervals between the marks. Coordinate values representing three-dimensional shapes at first and second portions of the object are converted respectively to coordinate values based upon a reference coordinate system identified by the marks. The coordinate values determined after the conversion are synthesized, so that data on the entire three-dimensional shape of the object is obtained.