The position detection apparatus includes a light projecting optical system which has an optical axis, and which cause 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 the optical axis direction, a detection unit which respectively detects the positions of the two light beams which have entered the light receiving unit, and a calculator which calculates the surface position of the substrate in the normal direction based on the positions of the two light beams, which are detected by the detection unit. At least one of the light projecting optical system and the light receiving optical system is shared for the two light beams.