This position detection apparatus includes a plurality of light receiving portions receiving a reflected laser beam from an indicator, a lens, a masking portion arranged between the light receiving portions and the lens, having a masking surface restricting the reflected laser beam guided to the light receiving portions in a direction orthogonal to a projection surface, and a determination portion determining a three-dimensional position in a projection image indicated by the indicator. The masking surface of the masking portion has such a concave shape that opposing ends thereof are closer to the lens than a central portion thereof.