To increase a load resisting strength of an installed lid surface by eliminating a movable element related to an opening/closing or detaching operation from component elements of a lid and forming an operating hole in a rigid disk as a lid detaching means, in a floor coupler in a building equipped with a central vacuum cleaner.

The lid 1 of the floor coupler X has a composite structure comprising a packing material 2 and the rigid disk 3. The packing material 2 has a plugging seal rib 21 elastically fitted in an open inner surface of a coupler body 4 so as to close a floor opening 41 throughout, and forms a diaphragmatic inner lid surface 11. The rigid disk 3 has the operating hole 31 bored by cutting of a part of a disk surface, and forms an outer lid surface 12 constituting a part of a load resisting floor by being elastically attached to an inner peripheral wall 22 of an installed outer surface of the plugging seal rib 21 of the packing material 2 and exposed into a building.