Patent ID: 7106452

Claim:
A measuring device comprising: a light source for emitting a linearly polarized light; polarization orientation setting means for switching the polarization orientation of the light flux from said light source means between at least two orientations and making the light flux exit; light re-combining means for re-combining light fluxes split from the light flux from said polarization orientation setting means after passing the light fluxes through an object to be measured and a reference surface; analyzing means for switching the polarization orientation so as to allow to pass only the same polarized component as the polarized light incident on the object to be measured; image pickup means for detecting interference information of the light which has passed through said analyzing means; and calculating means for calculating at least one of the average wavefront and the retardation of the object to be measured, on the basis of the interference information obtained when using the light in the two polarization states switched by said polarization orientation setting means.