To provide an ultrasonic vibration machining unit device and its working method realizing both improvement of machining performance and working efficiency and improvement of environmental protection over a wide range of small objects to large objects (small quantity of one article, large quantity of many articles, etc.) of boring work for many holes in a workpiece such as a fiber-reinforced resin.

The ultrasonic vibration machining unit device is configured to comprise: a rotary drive shaft means DS provided on a base part 1 in a manner advance-retreat is controllable; an ultrasonic vibration means 10 imparting ultrasonic vibration to a cutting tool T of the rotary drive shaft means in the rotating direction; a dust prevention means 20 surrounding the cutting tool and a main spindle tip part 6-the ultrasonic vibration means 10 and interlocking with advance-retreat movement of the cutting tool; a chip dust recovery means 30 flowing-in/exhausting an air current E into/from the dust prevention means and recovering chip dust C; an explosion-proof means 40 surrounding the rotary drive shaft means DS; and a dust recovery means 50 flowing-in/exhausting an air current E into/from the explosion-proof means and recovering resin dust J.