PURPOSE: To simply execute construction regardless of an installation place for a branch pipe by inserting a pipe holding ring or the like in an inside diameter enlarged portion of a socket provided in a socket connecting opening, screw- engaging a ring-shaped cap with the socket opening, and forming plural claws on the pipe holding ring.

CONSTITUTION: A cylindrical socket 30 is projected form the peripheral surface of a pipe 2, and a fit-in portion 38b is formed on the inside to prevent slip-off of the respective rings 35, 36, 37. When the tip of a pipe 12 is inserted in a connecting opening 2a, the pipe hits its tip against claws 35b of a pipe holding ring 35 and while the claws 35b are elastically deformed in the expanding direction, it is further inserted to be fitted to a pipe fit-in portion 33. The claws 35b bite the outer periphery of the pipe 12 to inhibit slipping off, thereby putting the pipe in such a connecting state not to be easily slipped off. Accordingly, the pipe can be surely connected to a branch pipe by simply operation of inserting the pipe in the connecting opening, and water-tightens can be kept by a seal ring 37. Further, the construction work in a job site for installing the branch pipe can be conducted simply and efficiently.