PURPOSE: To firmly fuse a main pipe and the saddle part of a branched saddle free from a gap, shorten the time for holding the branched saddle and the main pipe by a clamp, and reduce the necessary quantity of clamps,when the branched saddle (fused coupling) is joined with the main pipe.

CONSTITUTION: As for a branched saddle 8, the thickness of the center part 9b of a saddle part 9 joined with a main pipe P3 is formed thick, and the thickness at the edge part 9c is formed thin, and a main electric conductive heating body 11 is embedded in the inner peripheral surface at the center part 9b, and a subelectric conductive heating body 13 is embedded on the inner peripheral surface of the edge part 9c, and the main electric conductive heating body 11 and the subelectric conductive heating body 13 can be controlled separately. As for the joint, the branched saddle 8 and the main pipe P3 are clamping-held, and the subelectric conductive heating body 13 is electrically charged and fused and temporarily joined, and then a clamp is demounted after the temporary joint, and the main electric conductive heating body 11 us electrically charged, and fused and mainly joined.