PURPOSE: To obtain a device which expedites the change of a cage and balls and has a long effective by executing lubrication of a cage provided with a actuating member having a specific internal profile and all portions within the cage.

CONSTITUTION: The grooving device 1 for tubes includes a holding die 4 for holding a floating chuck 5 having a grooved chuck 6 into the correct position within the tube 2 to be grooved, a grooving unit including the rotary cage 8 enclosing balls 9 so as to form the internally grooved tube 2R and a finishing die. The radius of curvature of a supporting member 11 is at least the same as the radius of curvature of the balls 9 and the radius of curvature of a fixture 12 of the cage. The grooving device for tubes which lubricates between the balls 9 and the supporting member 11, between the balls 9 and the outside surface of the tube 2 to be grooved and the contact surface between the balls 9 themselves is provided.