PURPOSE: To make it possible to form a faucet of contracted diameter on the edge of a thermoplastic tube, by putting a plurality of heat resistant elastic rings side by side on the outer circumference of the edge of a tube of contracted diameter of a thermoplastic resin tube prepared by contracting the diameter by heating and softening, inserting a male mold into the edge of the contracted tube while being heated and enlarging thereby the inner diameter.

CONSTITUTION: A plurality of elastic rings 2, 2... are put on the outer circumference of the edge 11 of a tube of contracted diameter of a thermoplastic resin tube 1. Inner diameter of the elastic rings 2 are 90W95% of the outer diameter and an elastic ring 2 is set without gap in such a way that it is brought into contact with neighboring another elastic ring 2. The edge 11 of the tube of contracted diameter on which a plurality of elastic rings 2, 2... are put is immersed in a liquid paraffine bath of about 150°C for 5W10 min and a male mold 3 is inserted in said edge of the tube of contracted diameter. The edge of the tube of contracted diameter tends to expand its diameter larger than the outer diameter of the male mold. The inner shape of the edge 11 of the tube becomes to the outer shape of the male mold 3 by depressing the force which the edge 11 of the tube of contracted diameter generates owing to returning and expanding to its original shape by means of the elastic rings 2, 2....