PURPOSE: To improve handleability, transportability in a tube and to also improve operability in the case of compressing a sealing material.

CONSTITUTION: A cylindrical sealer 42 is disposed on inner peripheries of a pair of tubes 10, 12 to be connected by a joint. A backup element 46 is disposed on an inner periphery of the sealer 42, pressure fluid 66 is supplied to a cavity 50 of the element 46, and part of the element 46 is swelled. The sealer 42 is pressed to the inner peripheries of the tubes 10, 12 by the swelling to perform predetermined sealing performance. A test hydraulic pressure P0 is applied to a sealed air gap 68.