1. A surface shape measurement method that divides a surface shape of an object into a plurality of partial regions to obtain partial region data and that stitches the partial region data to measure the surface shape of the object, the method comprising the steps of: calculating sensitivity of an error generated by a relative movement between the object and a sensor for each of the partial regions; dividing the surface shape of the object into the plurality of partial regions to obtain the partial region data; obtaining the partial region data, calculating an amount corresponding to the error using the sensitivity; correcting the partial region data using the amount corresponding to the error; and stitching the corrected partial region data to calculate the surface shape of the object.