The manufacturing method of the invention manufactures a fuel filler pipe (branching pipe), where a breather pipe is branched off from a filler pipe main body. The manufacturing method extrudes a first extruded tubular member and a second extruded tubular member, conveys molds arranged on both sides of the first extruded tubular member and the second extruded tubular member, and forms the first extruded tubular member and the second extruded tubular member corresponding to molding surfaces of the molds, so as to mold the filler pipe main body and the breather pipe. The manufacturing method then thermally welds part of the second extruded tubular member with an outer wall of the first extruded tubular member and closes an opening end of the breather pipe to form a welding joint portion. A connection hole for connecting the conduit of the filler pipe main body with the conduit of the breather pipe is formed in the welding joint portion with a tool inserted through an opening of the filler pipe main body. This manufacturing method has excellent productivity and desirably reduces the manufacturing cost.