PURPOSE: To prevent a drill from being disabled and broken due to the chips clogging, by increasing the rigidity of the chip itself and permitting the chips to be discharged towards the outlet of a hole form a cutter part, by forming a cut or a groove on a rake surface and forming the cutter shape to a nonsingle straight line form.

CONSTITUTION: As for a twist drill 1 used for boring work, and old cutting edge 2 having a nearly straight line form is formed as shown by the two-point chained line, and a cut 3 is formed at htis part, and a new cutting edge 4 consisting of two straight lines is installed. Chips are generated in bending in the widgh direction by installing the new cutter 4, and curl is preventd. The rigidity is incrased because the chips are in bent form, and the chips are discharged toward the outlet of a hole from the cutting edge part, because of the presence of the free chips, and the working disabled state and the breakage of the twist drill due to the clogging of the chips are prevented.