PURPOSE: To lessen the possibility that the corner of a profile is cut and the generation of deflection for enhancing cutting accuracy by spirally providing quartered slits crossing at right angles at the center thereof to the portion from the tension grip entrance section of a bushing body to the intermediate position of an insertion section in the same direction.

CONSTITUTION: Quartered slits 4 crossing at right angles at the center thereof is spirally provided in the same direction from the invertedly tapered tension grip entrance section 2 of a bushing body 1 to the intermediate position of a cylindrical insertion section 3. The slits 4 may be made to be spiral being curved in the opposite direction at the intermediate section thereof, and the end section of the slits 4 may be made to be straight along the axis of the bushing body 1. Therefore, generation of the deflection in the bushing body 1 can be prevented by rotatably inserting a workpiece into the guide bushing 1, by adjusting the degree of tension gripping of the tension grip entrance section 2 by means of the female adjusting screw threadedly inserted into a male adjusting screw 6 so that the corner section of a profile may be prevented from entering the slits and by enclosingly supporting the workpiece, even if it is a round bar.