PURPOSE: To improve the cutting performance by a method wherein cutting chip produced is rolled up in a distorted groove, thereby being passed smoothly through the groove and prevented from being pressed against the groove.

CONSTITUTION: Cutting chip produced by a cutting blade 2 is sent into a distorted groove 4 along a rake face 21 and is rolled up here along the curvature of the cross section of the distorted groove. When the chip reaches the part of a projection 3, it is further rolled up with the radius of curvature of the projection 3 and then, getting over the projection 3, is sent toward the base part of a shank through the distorted groove 4 to be discharged. Since the cutting chip is rolled up to be as large as the radius r of cruvature, it is not pressed against the inner surface of the distorted groove 4 or that of a worked hole when it passes thrugh the distorted groove 4 having the radius R of curvature, thus being discharged smoothly.