PURPOSE: To increase hardness of a machined surface so as to improve wearing resistance and fatigue proof strength, by burnishing the machined surface while applying vibration to a mandrel, in the case of burnishing by a roll or a ball improving surface roughness or the like.

CONSTITUTION: When a suitable driving shaft 15 of drilling machine or the like is connected to a mandrel 1, an ultrasonic vibrating means 13 is interposed, and if a frame 3 is depressed against a spring, rollers 2, reducing a contour along the tapered part in the end of the mandrel, can be easily inserted into a machined part. Next, if the frame 3 is lifted, the rollers 2, spreading the contour, are adapted to an interval surface of the machined part to roll a machine surface while performing rolling motion. Here applying an ultrasonic wave, generated by an oscillator 14, to the mandrel 1 through the vibrating means 13, rotation and vibration are simultaneously given to increase machining efficiency. While by a shock effect due to the vibration, hardness of the machined surface is actively enhanced, improving also wearing resistance and fatigue proof strength.