PURPOSE: To prevent a locking ring from rotating in its tightening process so as to prevent a flexible tube from being twisted.

CONSTITUTION: A jointing device for tube comprises a joint main body 1 which is provided therein with a hole part 2 passing it in its axial direction and in which a flexible tube connecting hole part 9 provided with a step part formed in the middle position of the hole part 2, a locking ring 11 which is formed to wrap and engage with the top end of a flexible tube 10 and engage with the internal surface of the connecting hole part 9, and a tightening member 15 which is screwed into the joint main body 1 and presses the locking ring 11 to the inside of the connecting hole part 9. Also a groove part 5a into which the maximum diameter part of the locking ring 11 is fitted is formed in its axial direction in a female thread part which is extended to the outer end side in conjunction with the connecting hole part 9 and into which the tightening member 15 is screwed. Since the locking ring 11 is engaged with the internal surface of the connecting hole part 9 of the joint main body 1 when the tightening member 15 tightens by rotation, the locking ring makes no rotation following the process of tightening. Thus the flexible tube is prevented from being twisted.