PURPOSE: To simply produce a tube joint which connects tubes without backlash, securely obtains fixing of ring and corresponds to a diameter of tube.

CONSTITUTION: A punch 2 having a streak 3 appropriately formed in alternately different dimensions of a length in the pressing direction is inserted from one of opening end of a round tube 1 and the part from one of opening end to a prescribed position is roughly formed to a regular polygonal cross section of prescribed outer diameter. Successively, a ring 6 is externally fitted from other opening end and is arranged at the boundary between the part formed to rough regular polygonal cross section and part not formed. Subsequently, a punch 6 same as the punch 2 is inserted from other opening end, the part up to the position arranged with the ring 6 is formed to a rough regular polygonal cross section.