To make the cutting smooth and reduce the load to an edge by providing an ultrasonic vibration means for vibrating a circular saw supported by a rotating shaft to be drive and carrying out the cutting in the state of vibrating the circular saw.

A rotating shaft A supporting a circular saw 1 is constituted of cylindrical shafts 3, 3 connected together on a central shaft 2 through flanges 4, 4, and an ultrasonic vibrator B is fixed on the end of the central shaft 2. When a passive pulley 14 is driven by a driving motor, the central shaft 2 is rotated through the cylindrical shafts 3, 3 to rotate the circular saw 1. Also the ultrasonic vibrator B on the end of the central shaft 2 is rotated together. When an ultrasonic oscillator C is actuated in the above-said state, the vibration power is applied to the vibrator B is generate the ultrasonic vibration. The central shaft 2 is vibrated by the above arrangement, and the circular saw 1 is also vibrated by a given deflection curve. As the rotating shaft A is supported by the flanges 4, 4 by the nodes of vibration and the circular saw 1 is also retained by flanges 7 and 8 by the nodes of vibration, the attenuation of vibration is not generated.