PURPOSE: To surely stick a saddle central part with pressure so as to prevent generation of defective fusion by fastening the central part of the saddle to a plastic pipe by a bolt when a plastic branch pipe joint is fixed temporarily to the plastic pipe.

CONSTITUTION: A branch pipe joint A is pressed against a pipe C and fitted on the outer peripheral face of the pipe C from a space of fastening sections 10 by pushing a saddle 2 to open it. The fastening parts 10 opposed on the outer periphery of the pipe C are fastened by a bolt 15 and a nut 16, the central part of the saddle 2 is fastened to the pipe C, and the branch pipe joint A is fixed temporarily to the pipe C. Thereafter, a connector of a controller 17 is connected to a mat-like heating element embedded in the saddle 2 and the saddle 2 is electrically fused on the outer peripheral face of the pipe C. Next, a drill 18 is inserted into a joint 1, a hole 19 is formed on the outer peripheral face of the pipe C, and the joint 1 is communicated with the pipe C. After a branch pipe B is inserted into a socket 5 of the joint 1, the connector of the controller 17 is connected to a cylindrical heating element 6 at the end face of the socket 5, and the socket 5 is electrically fused on the outer peripheral face of the branch pipe B so as to joint.