Patent ID: 7391521

Claim:
A position detection apparatus comprising: a beam splitter arranged to separate an incident beam into a first beam and a second beam and to supply the first and second beams to a reference surface and a measurement target surface respectively; an optical unit arranged to lead a beam from a light source to said beam splitter so that the first and second beams obtained by said beam splitter are respectively incident upon the reference surface and the measurement target surface at an angle, and to lead the first and second beams which have been integrated by said beam splitter after being reflected at the reference surface and the measurement target surface respectively, to a reflecting member; and a light receiving element arranged to receive the first and second beams and generate an interference signal, wherein the first and second beams reflected at said reflecting member are led to said beam splitter by said optical unit, separated again by said beam splitter, reflected at the reference surface and the measurement target surface respectively, and integrated again by said beam splitter, said optical unit leads the first and second beams which have been integrated again by said beam splitter to said light receiving unit, said light receiving element receives the first and second beams from said optical unit and generates the interference signal corresponding to a phase difference of the first and second beams, and said optical unit focuses the first and second beams which have been integrated by said beam splitter at the position of said reflecting member.