To prevent the irregularity of caulking from occurring by inclining a caulking jig toward the direction as same as the axial length direction against the cross-section of including the circumference that the longitudinal direction of the end face is crossed almost orthogonally against the axial length direction of a connecting cylinder, and caulking with over-lapping mutually adjoining end faces to the width direction.

A plane shape of an end face of each caulking jig 33a is made in a rectangular shape whose long side has a prescribed inclining angle θ against the plane to include the circle of internal circumference to close a connecting cylinder to be caulked of a ring part 31a. On the result, an adjoining caulking jigs 33a are not collided mutually to the neighborhood of the center, and these are made to be lapped to the direction that the end face is crossed to the longitudinal direction when these are projected some degree. The end face is made in a shape having a curved face along the connecting cylinder to be executed with caulking. On the result, the irregularity of caulking is not generated in the direction of circumference, the contact pressure of the connecting cylinder and an elastic tube is uniformed and the sealing performance is improved.