To certainly prevent separation of two pipes by forming a projected part on an outer surface of an insertion port of the other pipe at a position separated from a faucet of one pipe and providing the other end of a separation preventive member one end of which is mechanically connected to the faucet on the projected part free to engage with it.

An insertion port 14 on which a projected part 19 is formed and a sealant 15 is fastened is inserted into a faucet 12 on which a projected part 20 is formed at the time of jointing pipes 11, 13 with each other. At this time, the sealant 15 is guided by a tapered surface 17 and enters the inside of the faucet 12, compressed between the faucet 12 and the insertion port 14 and displays a required sealing function. After the insertion port 14 is inserted into the faucet 12, flanges 23, 24 are externally fit on these insertion port 14 and faucet 12, a bolt 28 is passed through these flanges 23, 24, it is fastened against a nut 29, and accordingly, the flange 24 is engaged with the projected part 20, the flange 23 is engaged with the projected part 19 at a position at a distance D from an end surface of the faucet 12, and separation of both of the pipes 11, 13 is prevented.