Patent ID: 8363230

Claim:
A displacement detecting device comprising: a light source; a first beam splitter adapted to split the light emitted from the light source into a first beam and a second beam; a reflecting member adapted to reflect the first beam split by the first beam splitter; an objective lens adapted to condense the second beam split by the first beam splitter on a surface-to-be-measured; a first light receiving section adapted to receive interference light of the first beam reflected by the reflecting member and the second beam reflected by the surface-to-be-measured; a relative position information output section adapted to output relative position information in height direction of the surface-to-be-measured based on intensity of the interference light received by the first light receiving section; a second beam splitter adapted to extract a part of the second beam reflected by the surface-to-be-measured; an astigmatism generator adapted to generate astigmatism in the second beam extracted by the second beam splitter; a second light receiving section adapted to receive the second beam having the astigmatism generated therein by the astigmatism generator; and an absolute position information output section adapted to generate absolute position information in height direction of the surface-to-be-measured based on intensity of the received light detected by the second light receiving section, and output the generated absolute position information.