PURPOSE: To improve a soft tubular member in its insertion quality to a hard tubular member further contriving the prevention of the soft tubular member from its break in the time of use by inserting the other tubular member, consisting of relatively soft plastic, into an annular void, formed between male and female mold parts, to be closely mounted.

CONSTITUTION: A hub 16 consists of relatively hard plastic, comprising a tubular female mold part 16A and a male mold part 16B which is coaxially provided with a predetermined space in the inside of the female mold part 16A while protruding to the outer from its end face, and the hub 16 forms an annular void between the female mold part 16A and the male mold part 16B. A tube 17, consisting of relatively soft plastic, is provided with an external diametric part 17A connected to decreasing its diameter by the female mold part 16A and an internal diametric part 17B connected to spreading its diameter by the male mold part 16B. Thus inserting the tube 17 into the annular void formed between the female mold part 16A and the male mold part 16B of the hub 16, it is connected to the tube 17 liquid-tightly and air-tightly by blocking respectively the female mold part 16A to the external diametric part 17A and the male mold part 16B to the internal diametric part 17B.