A guide tapered surface 17 of a pipe coupling port 16 has a small diameter portion 17a guiding to a distal end portion 3a of a bite type sleeve 3 to bite into a coupling pipe 5 and a large diameter portion 17b sealing a tapered outer circumferential surface 33 of the bite type sleeve 3 by making close contact with the tapered outer circumferential surface 33 of the bite type sleeve 3. A tilt angle α1 of the small diameter portion 17a relative to a central axis of the guide tapered surface 17 is greater than a tilt angle α2 of the large diameter portion 17b relative to the central axis. Therefore, even when a distal end portion of the coupling pipe 5 is not inserted up to an innermost portion of the pipe coupling port 16, excellent sealing performance is obtained in a portion coupled to the coupling pipe.