PURPOSE: To enable super-precision boring to be carried out without any exothermic reaction by overlapping torsional supersonic vibration and axial vibration of tool shaft lower than said vibration for vibration cut on a tool to cut off chips and work a hole with wave form of intermittent pulse cutting force.

CONSTITUTION: A drill end is subjected to supersonic torsional vibration with vibration frequency f and amplitude a in the direction E and a unit body 21 is secured fixedly to a guide roller 30 guided by steel balls provided on a carriage 29, and coupled with an electro-hydraulic system vibrational drive unit 32 through a connecting rod 31 so that pressurized oil from a hydraulic unit 34 is alternately changed over by a servo valve 33 in a control unit 35 to vibrate the drill with about 2W200Hz of vibration frequency vibration frequency f and amplitude in the direction D and A. Namely, a workpiece 36 is mounted on a chuck 37, and a supersonic oscillator 27, the hydraulic unit 34 and control unit 35 are operated to give supersonic torsional vibration and rotation simultaneously to the drill and give a feed S to the drill vibrating axially with low frequency vibration in the direction of arrow 38 so that precision boring can be carried out.