A position detector configured to detect a position of an object to be detected. The position detector has an optical system configured to detect a mark on the object to be detected that includes a lens that has a positive refractive power, and a reflection member configured to reflect a light flux that passes through the lens in a convergent state or a divergent state. The reflection member is configured from at least one material of a material that exhibits a refractive index of less than 1.0 and an extinction coefficient of greater than 0.0, and a material that exhibits a refractive index of greater than 1.0 and an extinction coefficient of greater than 0.5.