PURPOSE: To make it needless to provide an O ring as a seal member at various parts on the peripheral surface on the side of a hollow stem by providing an installation part to fit closely on the inner peripheral surface of an edge part ring as well as providing an installation part to fit closely on the inner peripheral edge part of an installation ring of a tube coupling main body.

CONSTITUTION: An installation ring 10 of a tube coupling 1 is inserted into a hollow stem 4, and one edge part of the inner peripheral surface of the installation ring 10 of the tube coupling main body 1 is fit tightly to an installation part 42 of the hollow stem 4. Next, a middle ring 2 is inserted into the hollow stem 4, and a connec tion part 20 on one edge of the middle ring 2 is fit tightly to the other edge part of the inner peripheral surface of the installation ring 10 of the tube coupling main body 1. Additionally, a necessary number of the tube coupling main bodies 1 and the middle ring 2 are inserted into the hollow stem 4 reciprocally, one edge part on the inner peripheral surface of the installation ring 10 of the tube coupling main body 1 is tightly fit to the connection part 20 of the other edge and the connection part 20 of one edge of the middle ring 2 is tightly fit to the other edge part on the inner peripheral surface of the installation ring 10 of the coupling main body 1. Thereafter, an edge part ring 3 is tightly fit to the hollow stem 4 and the installation ring 10.