To keep cutting balance before and after diameter regulation in a throw-away type drill having a diameter regulating mechanism capable of regulating the outer diameter of the drill.

In this drill with the diameter regulating mechanism, throw-away tips having a cutting edge are arranged at the tops of a pair of chip discharge grooves, and the same number of throw-away tips are arranged facing to each chip discharge groove. The outer diameter of the drill is regulated by moving, in the diameter direction, only the throw-away tips having an outer peripheral blade disposed outermost side in the diameter direction. In the drill with the diameter regulating mechanism, cut width between faced cutting edges does not change before and after regulation of the outer diameter of the drill, so that the cutting balance is kept and stable drilling is performed.