To facilitate position adjustment of a pair of photo-interrupters constituted by being integrated with a pulsar in order to detect the moving direction and the moving quantity of a moving element.

A plurality of slits 49A are formed at prescribed intervals along the circumferential direction on the peripheral part of the pulsar 49. Detection parts 92A, 93A of the photo-interrupters 92, 93 are positioned so that a part where the slit 49A is formed is interposed between a light emitting element and a light receiving element. The photo-interrupters 92, 93 are supported rotatably by positioning screws 95, 96. An adjusting member 94 is arranged between the photo-interrupters 92, 93 so as to be rust-jointed on the photo-interrupters 92, 93. An adjusting screw 91 is screwed with a penetration hole 80c of a loading part 80 and also screwed with a penetration hole 941A of a screw accepting part 941 of the adjusting member 94.