PURPOSE: To make the inner tube and outer tube fixed to each other with good strength and in a stabilized state.

CONSTITUTION: A piece of shrink film 7 preliminarily coated on the inner surface with an adhesive and formed into a tube though drying is placed over a joint of an inner tube 1 and an outer tube 2 where the two are fitted with each other. By heating the shrink film 7 is made to contract and the inner tube 1 and the outer tube 2 are fixed to each other by the action of the adhesive. When a shrink film 7 with no coating of the adhesive is in use, this process is preceded by winding of an adhesive tape 9 of thermoplastic resin on the inner tube or the outer tube. The shrink film 7 and the adhesive tape 9 are integrally joined under heat.