A position detecting apparatus includes a first illuminating unit that radiates light onto a substrate in a direction substantially parallel to the front and the rear surfaces of the substrate from the direction of a lateral face of the substrate; a second illuminating unit that radiates light onto the front surface of the substrate, in a direction substantially perpendicular to the front surface of the substrate; an image pickup unit that takes an image of the substrate from a rear surface side thereof; and an edge-position detecting unit that detects an edge position of the substrate, based on a first image that is taken while the light is being radiated from the first illuminating unit and a second image that is taken while the light is being radiated from the second illuminating unit, respectively.