To realize simple and reliable attaching and detaching by pushing and pulling the center part of an elastic plate (3) in the state of a leaf spring in vertical directions.

By pushing and pulling the center part of the flat resilient plate (3) in vertical directions to bend the resilient plate (3), the length of the resilient plate (3) in a straight line to the right and left is varied to withdraw or project both of the ends of the resilient plate (3) inward and outward through both of the opening parts on the side faces of a projecting part (2) supporting the vicinities of both of the ends of the elastic plate (3), so as to pass through a narrowed place at the upper part of the opening part of a recessed part (1) or to stop there for attaching or removing.