The purpose of the present invention is to provide a stopper capable of easily inserting a sealing member 3 into a stopper member 2 and also capable of preventing the sealing member 3 from coming out of the stopper member 2. The stopper is equipped with a stopper main body 1 having a guiding path 10 extending in an axial direction, a stopper member 2 having a flow path extending in the axial direction and inserted in the guiding path 10 of the stopper main body 1, and a sealing member 3 inserted into the flow path 20 of the stopper member 2 in such a manner as to block the flow path 20. The stopper member 2 is equipped with, at a position where the sealing member 3 is inserted, a first peripheral wall section 27 fixed in a manner as to extend in the axial direction and a second peripheral wall section 27 divided in a manner as to open radially outward along the axial direction.
