To enable polyethylene pipes to be connected together with a short polyethylene cylinder in which a heating element is not buried.

The tubular end part of each of polyethylene pipes 3 is inserted into the open part of a short polyethylene cylinder 4 to bring the outer peripheral wall of the polyethylene pipe 3 into contact with the inner peripheral wall of the short polyethylene cylinder 4. At the same time, the outer peripheral face of the tubular end part of the polyethylene pipe 3 and the inner peripheral face of the short polyethylene cylinder 4 are fused together by rotating the short polyethylene cylinder 4 at its cylindrical shaft as a rotating pivot while the polyethylene pipe 3 is pressed toward the short polyethylene cylinder 4. Next, the rotation of the short polyethylene cylinder 4 is stopped to weld the outer peripheral wall of the tubular end part of the polyethylene pipe 3 to the inner peripheral wall of the short polyethylene cylinder 4.