A partial spherical shape of each measurement area of a sphere to be measured, which is established so as to have an area overlapping with another measurement area adjacent to each other, is measured at each rotation position, and the surface shape is measured by joining the partial spherical shapes of the measurement areas by a stitching operation based on the shape of the overlapping area. The position at which the sphere is measured is changed and re-held. A positional displacement between half parts of the sphere before and after re-holding, which is caused by an effect of an error owing to the re-holding, is separated into three rotational components. Magnitudes of the three rotational components are quantified by image correlation and the positional displacement corrected. Then, the stitching operation is performed to measure the entire part of the sphere surface.