To facilitate vertical optical axis alignment of laterally set sensors while dispensing with processing of a hole part or the like for mounting an area sensor on a guide rail of an opening and closing body to reduce the processing man-hours.

A pair of guide sides forming a guide groove part for receiving the end side of a moving body is formed on a guide rail in opposition to a building opening part, one of the guide sides includes a recessed groove longitudinally extended to face the building opening part, and a detector is installed to the recessed groove.