To suppress vibration during cutting so as to perform highly accurate beveling work by aligning the inclined attitude of a plurality of cutting heads as much as possible to set these in good balance.

A plurality of cutting heads 2a and 2b capable of adjusting inclining angles are disposed in a running base, and first and second cutters 3a and 3a attached to these cutting heads 2a and 2b are set to correspond to the upper and lower edge parts of a machined material W. The cutting edge tips of the cutters 3a and 3b are composed of bottom and outer peripheral cutters (m) and (n), and the cutting edge tips of the cutters 3a and 3b are selectively used according to beveling angles. By such selective use, the inclined moving range of the cutters 3a and 3b is made small, and the inclined attitude of the plurality of cutting heads 2a and 2b are aligned as much as possible and set.