To precisely measure the shape of a prescribed area on the surface of an object.

The position information for the surface of the object W relative to the normal direction of the surface of the object W is measured along a plurality routes extending from each of a plurality of points PnS (n=1-4) on the surface of the object W to the outside of the object. Consequently, for each of the routes, a measurement waveform characteristically changed in the boundary of the prescribed area with the other area is obtained. The measurement result is successively analyzed, whereby the boundary point position of the intended prescribed area with the other area is determined by the number of the routes. The shape of the prescribed area is specified from the determined boundary point positions. Accordingly, the shape of the prescribed area on the surface of the object W can be precisely measured.