A position measurement system optically measures a position of an object in a simple manner at low cost. The position measurement system includes: a light source; an optical lens with a large spherical aberration which transmits light from the light source and forms a light ring due to its spherical aberration; a light receiving device (CCD sensor) which detects the light ring as formed by the optical lens; and a calculator which measures a position of the light source according to detected information on the light ring as detected by the CCD sensor. An optical mirror with a large spherical aberration may be used instead of the optical lens.