In a position detection system, a retroreflection portion is provided on an outer peripheral surface of a designating member. Alight source unit emits detection light along an imaginary plane parallel to a reference surface. A light receiving element is arranged on one side in a Z-axis direction from the imaginary surface in such a way that a direction of a normal light to a light receiving surface intersects with the reference surface. When a distance between the designating member and the light source unit is long, light reflected by the retroreflection portion becomes incident more efficiently on the light receiving surface of the light receiving element than when the distance is short.