A radio-wave transmitter-receiver section (12) forms a radio-wave detection zone (16) for detecting an object at a location way from a door (4). A light emitter-receiver section (20) forms an optical detection zone (42) for detecting an object at a location along and closer to the door (4). The light emitter-receiver section (20) includes mirrors (28, 36) which are used to increase or decrease the depth dimension of the optical detection zone (42) in the direction perpendicular to the door (4).