A two-dimensional position detecting device includes a movable member which relatively moves parallel to a stationary member; a light source and a two-dimensional position sensor which are fixed to one and the other of the stationary member and the movable member, respectively, the two-dimensional position sensor receiving light emitted from the light source to detect a light-receiving point on a light receiving surface of the two-dimensional position sensor; and a reducing projector optical system, positioned between the light source and the two-dimensional position sensor, for converging the light that is emitted from the light source on the light receiving surface of the two-dimensional position sensor.