PURPOSE: To measure an object surface which has a large aperture ratio by making a spherical wave incident on a hologram and also using a diffracted component of (+n)th order.

CONSTITUTION: Laser light projected from the final surface 4a of a reference converging lens 4 passes through a filter 5 arranged at the focus position of a lens 4 and also passes through the hologram 6 to impinge on the surface 7 to be measured which is a concave aspherical surface. When a spherical wave is incident, the hologram 6 is a zone plate type hologram where such a pattern that the diffracted component of +1st order has a wave front in an ideal aspherical surface shape at the position of the surface 7 to be measured is drawn. The laser light incident on the surface 7 to be measured is reflected by the surface 7 and diffracted again by the hologram 6 to reach the filter 5. At this time, only diffracted light containing measured surface information, i.e. diffracted component of +1st order in the light reflected by the surface 7 to be measured passes through the filter 5 and the remainder is cut off. Consequently, the contrast of interference fringes is increased and accurate measurement is performed.