PURPOSE: To manufacture the connecting tube at low cost by the simple apparatus and operation, by working the tube when being still hot and forming simultaneously the fusion-bonding part at the tube wall in time of making tubular film by the inflation process.

CONSTITUTION: A pair of sealers 5, 6 is arranged following the inflation die 3. Thermoplastic resin melt-extruded tube-like from the die 3 is formed into the tube 1d by inflation, and on the way of pulling up the obtained tube 1d which is being cooled by air from the air ring 4, also before perfectly hardening tube 1d is pressed from the both sides by a pair of sealers 5, 6 which rotate at the same peripheral speed as the ascending speed of the tube 1d. By this, the fusion bonding part 1c is formed and the tube 1a and 1b are formed in parallel at the both sides. Then, those are cooled and hardened by blasting air from the air pipes 32, 33 and the connecting tube 1 composed of the tube 1a and 1b is formed and taken up via the nip rolls.