Provided are a housing (8) that includes a stopper section fitting portion (13) into which a treatment instrument stopper is inserted at the upper end of the housing, an engagement portion (19) which is fitted to a channel opening (6) at the lower end of the housing, a tab (14) which is held when the housing is removed from the channel opening, and a notch groove (15) which is torn by a pullup operation a first stopper section (9) that has a first treatment instrument insertion hole (11) which is provided in the housing (8) so as to come into contact with the channel opening and into which a treatment instrument is inserted and a second stopper section (10) that has a second treatment instrument insertion hole (25) which is provided in the housing (8) so that the end of second treatment instrument comes into contact with the opening of the first stopper section (9) and into which the treatment instrument is inserted.
