A thermoplastic resin tube 30 is a tubular body opened at both ends, and the step for forming the tube 30 is conducted by using a material (preferably having flexibility), for example, thermoplastic resin such as polyolefin such as polyethylene, polypropylene, ethylene--propylene copolymer, ethylene--vinyl acetate copolymer and cross-linked ethylene--vinyl acetate copolymer, polyvinyl chloride and