PURPOSE: To provide a tube fitting which has no risk of generating a crack even when a flexible tube is bent.

CONSTITUTION: A tube fitting comprises a fitting main body 1 provided with a flange part 11 almost at the center, a connection part 12 at one end, a cylindrical guide part 13 at the other end, and a male screw 15 provided at its depth, and a box nut 2 provided with a female thread 21 to be threaded with the male screw of the fitting main body 1 at a forward end inner circumference, and an inverse taper part 22 at a base part inner circumference. By theading the box nut 2 into the male screw 15 of the fitting main body 1, and pressing the inverse taper part 22 of the box nut 2 inward, a connection tube 3 engaged with the cylindrical guide part 13 of the fitting main body 1 is pressurized in the tube fitting, where a base part forward end of the box nut 2 is protruded toward the side from a forward end of the cylindrical guide part 13 of the fitting main body 1.