To solve a problem that, normally, when drilling to a depth which is about seven times as large as a diameter of a boring bar body shank, chattering vibration is easily generated, in particular, drilling for an inner diameter of 30 mm or less becomes difficult, therefore various vibration-proof tools have been developed, but many of them are complicate in structure or use expensive materials and are extremely expensive, and an inexpensive tool is desired.

Bending vibration during cutting is converted to torsional vibration by a simple structure formed of three items of a boring bar body shank. a shaft integrated with cutting edges and a sleeve, so that vibration of the body shank is suppressed and the generated torsional vibration is suppressed by a dynamic vibration reducer.