An apparatus for measuring an object's surface shape that obtains complex amplitude
at a plurality of positions substantially in the directions of the optical axis
of the light reflected by the object and calculates the first surface shape of
the object by the depth-from-focus principle. On the other hand, using the phase
data of the complex amplitude, the apparatus can measure a micro shape in the sub-fringe
order by ordinary laser interference measurement. The first surface shape data
are applied to a region including a step of a height greater than of the
light's wavelength and second surface shape data are applied to the other region.
