Position detection apparatus and exposure apparatus

A position detection apparatus comprising:

• a light projecting optical system which has an optical axis, and which causes two light beams symmetrical about the optical axis to enter a substrate;
• a light receiving optical system which receives the two light beams which have emerged from the light projecting optical system and are reflected by the substrate;
• a light receiving unit which is arranged at a position shifted in an optical axis direction of the light receiving optical system from an imaging plane of the substrate set by the light receiving optical system;
• a detection unit which respectively detects positions of the two light beams which have entered the light receiving unit;
• and
• a calculator which calculates a surface position of the substrate in a normal direction based on the positions of the two light beams, which are detected by the detection unit,
• wherein at least one of the light projecting optical system and the light receiving optical system is shared for the two light beams.