PURPOSE: To retrench the production cost of a helical rack bar with different directions of tooth twisting, or the like, by making it possible to process the helical rack bar while changing the direction of tooth twisting, without replacing a guide.

CONSTITUTION: A workpiece not shown in the drawing is held by a work chuck 11. A work carrier 5 is moved by a radial feed motor 6 so that the workpiece is placed at the front or rear portion of the axis of a cutting spindle 3. A feed table 9 is disposed in a prescribed position. Motors 13, 15 are then driven under numerical control, at the same time as each other, depending on the reciprocation of a pinion cutter 4, to subject the workpiece to an axial feed and a circumferential rotation simultaneously so as to shape helical teeth sequentially.