PURPOSE: To permit cutting in high efficiency by using both of the turning method for cutting a turning workpiece and the milling method for cutting a fixed workpiece with a number of rotary blades, when a metal material such as round bar, pipe etc. is cut.

CONSTITUTION: When a pipe is cut, a cut part is formed by the thickness of the pipe by revolving a saw, and then a work is revolved slowly, and the pipe is cut. In this case, the milling process is adopted, and a cutting region has a length corresponding to a width (a). While, when cut is carriedout with a saw having chips 2 arranged on the inner periphery of a dougnut-shaped substratun 1, the cutting region is the circular part corresponding to a width (b), and the cutting region increases. That is, cutting of workpiece is more efficient by use of a doughnut-shaped inner peripheral saw than by use of a round saw.