A forceps plug includes a tubular plug main body, and a tubular fixing member rotatably held on the outer periphery of the plug main body. The inner peripheral surface of the fixing member is provided with a pair engaging claws. A ratchet mechanism that allows the fixing member to move to an incorporated location, an attachment position, a fixed position, and a removal position in order, but stops further movement to a position where the fixing member has moved once is provided between the inner peripheral surface of the plug main body and the outer peripheral surface of the fixing member. Since the fixing member of the used forceps plug removed from a opening is stopped from being to the fixed position by the ratchet mechanism, the fixing member cannot be fixed to the opening. Reuse of the used forceps plug can be made impossible without being accompanied by destruction.
