PURPOSE: To heighten bending rigidity and torsional rigidity of a root part of a drill by forming a web of a chip space, which extends from the end of a parallel web part to the root of the drill, into a tapered web in which the thickness uniformly increases toward the root.

CONSTITUTION: The shape of a web of a chip space at the tip of a drill 1 is formed into a tapered web 2 in which the thickness uniformly increases from the tip toward the root, while the shape of a web of a chip space at the intermediate part continued from the web 2 of the drill 1 is formed into a parallel web 3 in which the thickness remains constant. In addition, the web of a chip space extending from this parallel web part 3 to the root of the drill 1 is formed into a tapered web 4 in which the thickness uniformly increases toward the root. Accordingly, both torsional and bending rigidity can be heightened, and at the same time chip blocking can be prevented.