To form a joint body and a boring cutter into a small and compact form each, and takeout a branch pipe having a great flow rate without lowering the strength of a main pipe.

This joint and a cutter are formed out of a joint main body composed of a saddle part 21 to be connected with the surface of a main pipe 40 made out of synthetic resin, a branch pipe part 23 branching off out of the saddle part 21 while being intersected with the axial line of the main pipe 40, and of a boring pipe part 22 interposed between the saddle part 21 and the branch pipe part 23, and of the cutter 30 in the non-cylindrical shape in cross section of a blade part, which carries out boring in such a way as to cut out the side part of the main pipe out of the boring pipe part of the joint main body, and the main pipe 40 is bored by the cutter 30 first so as to let its branch be taken out of the main pipe 40 into the branch pipe part 23. The cutter 30 is to be formed into a non-cylindrical shape so as to allow boring to be made long in the longer direction of the main pipe 40, and to be made short in its radial direction.