To enable the connection of a pipe to a mating member through one-touch operation by simply inserting the pipe into a mounting hole of the mating member without a screwing means, and to prevent a retainer from bending against pulling force acting on the pipe and thereby to prevent damage of the pipe and falling-off of the pipe.

An outer face of an insertion hole 3 of the pipe 2 is an abutting portion 4 against an O-ring flare disposed to a pipe 2, and engagement step portions 11 engaged to engagement projecting portions 12 formed to an inner face of the mounting hole 10 of the mating member 8 to be connected are disposed, so that a retainer body 1 is formed. A socket member 13, which is detachably inserted between opposite inside faces of the tapered pieces 5 of the retainer body 1 to make the tapered pieces 5 brought into close-contact with the inner face of the mounting hole 10 of the mating member 8, is provided.