1. A surface shape measurement method for measuring a surface shape of an object, the method comprising the steps of: dividing, using a processor, the surface shape of the object into a plurality of partial regions; obtaining, from a sensor, partial region data regarding the surface shape of the object for each partial region; calculating, using the processor, sensitivities of the partial region data with respect to relative movements between the object and the sensor for the partial regions; calculating, using the processor, amounts corresponding to errors generated by the relative movements using the calculated sensitivities; correcting, using the processor, the partial region data using the calculated amounts corresponding to the errors; and stitching, using the processor, the corrected partial region data to determine the surface shape of the object, wherein each of the sensitivities is a sensitivity of a wavefront slope distribution on the sensor with respect to a relative drive error between the object and the sensor, and wherein each of the sensitivities is calculated based on a difference between data determined before and after the relative movement between the object and the sensor by a predetermined amount.