PURPOSE: To surely cut chips and to continuously and safely discharge these to the outside by providing cutter sections engaged with drills between a drill guiding section and a jig fitting section.

CONSTITUTION: A jig is placed on a boring-machined workpiece, the jig fitting section 1 of a chip cutting bush B is fitted into the jig, a drill edge is fitted into the drill hole section 21 of a drill guiding section 2 and fitted into the fitting hole section 11 of the jig fitting section 1. Then, when the drill edge is rotated, since a gap section in a longitudinal direction is formed almost twice as large as the drill outer diameter of the drill edge and a cutter section 3 is disposed in a plan view almost on the same side relative to a center shaft, an opening can be widely formed. Thus, chips are finely cut between the drill edge and a cutter 32 without any remaining and safely discharged to the outside.