PURPOSE: To provide stable seal face pressure for a long time by inserting a bellows flexible pipe from a socket in a nut, moving a sleeve to the corner side via a packing, releasing snap rings from being held by a locking pawl on the sleeve and shrinking the snap ring side.

CONSTITUTION: When a flexible pipe 7 is inserted from a socket 21 in a nut 2 after assembled as shown in the upper half of Fig., the first mountain of the flexible pipe 7 is put in contact with the corner end of a packing 3 and moved to the corner side while keeping the outer periphery sealed. As the packing 3 is in one unit with a sleeve 4, the sleeve 4 is moved together, but snap rings which are prevented from being moved are left and a locking pawl staying between the snap rings 5 is pulled out and disengaged from the sleeve 4. In this way, the snap rings 5 are moved while being shrinked by the shrinking force of an O-ring 6 and fitted to the valley of the flexible pipe 7. Then, connection is completed by additionally fastening the nut.