PURPOSE: To have movement of a bushing without causing transverse swing, even though the resistances to the traveling tool rests differ by retaining the inner race of a thrust bearing at the periphery of the rotor and by putting the inside surface in engagement with the slide bushing in such a way as easy to slide.

CONSTITUTION: A thrust bearing 5 is held by a housing 4, which is fastened to the shaft end of a rod 3 of a drive cylinder 2. Power is transmitted to a rotor gear 7 through a belt 6 to rotate the rotor 9. A slide bushing 10 is put in engagement with the periphery of the boss part of rotor 9 in such a way as easy to slide to each other, and the periphery of bushing holds the inner race of thrust bearing 5 in such a manner that the thrust force can be transmitted during rotation, so that movement will be made on receiving the thrust force of rod 3. Bushing 10, pinion 12 and tool rest 14 are moved, and the work is given a depth cut by a cutter 15. Here the bushing can travel without transverse swing even though resistances to the moving tool rests differ.