Coordinate transformation parameters are adopted at the time of synthetically combining partial measurement data so as to eliminate the setting error that can get in when a workpiece is set in position on a measuring machine. Then, a shape parameter is adopted to estimate the approximate error shape of the entire workpiece and the approximate error shape is removed from the measurement data. As a result, the residuals are reduced if the measurement data are those of three-dimensional sequences of points. Differences are small when small residuals are compared so that the mismatch is reduced. According to the present invention, the entire measurement data can be synthetically combined without using the conventional concept of overlap.