Abstract: An insertion protrusion of a frame of a device is inserted into an opening in a wall. A first fastening portion of the frame faces a first wall surface of the wall. A first screw member inserted into an insertion hole in the insertion protrusion is threadedly engaged with a second screw member on a screw axis. By operating an operating portion of an operating mechanism, the operating portion exposable from the frame toward a first direction, a rotational position of the second screw member about the screw axis can be controlled between a first rotational position and a second rotational position. The wall is fastened directly or indirectly between the first fastening portion of the frame and a second fastening portion of the second screw member having been displaced to the first rotational position.