A position detecting system has a transport device, a light source, at least one optical element, a reflective member, a drive unit, and a controller. The transport device transports and places an object on a placement table. The light source generates measurement light. The optical element projects the measurement light, as projection light, generated by the light source and receives reflected light. The reflective member is disposed on the transport device. The reflective member reflects the projection light toward the placement table, and reflects the reflected light of the projection light, which is projected toward the placement table, toward the optical element. The drive unit operates the transport device so that the reflective member scans a plurality of linear scanning ranges. The controller calculates positional relationship between the focus ring and the object placed on the placement table based on the reflected light within the plurality of linear scanning ranges.