To ensure high watertightness by providing a locking means comprising a rugged part at the peripheral surface of the end connection part of a pipe, elastically fitting and locking a large diameter packing material to the locking means, and making the packing material act as a locking part when connecting a supply/drain pipe to a sink or the like.

When connecting the drain pipe 1 made of polyvinyl chloride or polypropylene to a drain port fitting 102 locked to the drain port edge of a vessel body such as sink and a wash basin by a box nut (a connecting member) 103, the locking means 11 comprising a rugged part is provided at the peripheral surface of the end connection part of the drain pipe 1, and the large diameter packing material 2 is elastically fitted and locked to the locking means 11. The packing material 2 is formed by integrally providing a collar-like packing part 2' annularly protruded on the outside of the annular protruding part of the locking means 11. The box nut 103 fitted to the outside of the packing material 2 is thread-fastened to the drain port fitting 102 to press the collar-like packing part 2', which is elastically deformed to obtain excellent water stop performance.