A position detection apparatus that illuminates light from a light source unit onto an object and that receives reflected light from the object on a light receiver to detect position information of the object, includes a detector (10) and a signal processor (102), the detector includes a first grating (15) in an optical path between the light source unit and the object, a second grating (16) in an optical path between the object and the light receiver, and a third grating (17) in an optical path between the second grating and the light receiver, the signal processor acquires the position information of the object based on a phase variation of the second periodic image detected by the light receiver, and the position information of the object is information related to a distance from the detector to the object.