To gradually intensify/reduce contact pressure between each tooth and a cut material and to bring the tooth into strong contact with the cut material even with small pressing force to increase cutting force by forming a rotary saw provided with a large number of teeth at the specified pitch at the outer peripheral part of a disc-shaped base metal, in a non-complete circle with respect to a rotation axis.

When a cut material is cut in the rotating state of a rotary saw 1 through a rotating shaft 10, the rotary saw 1 is eccentrically rotated with an eccentric quantity H to the rotation axis C1 of the rotating shaft 10, and teeth 4 gradually fluctuate in a radial direction within a range of 0.5 mm at the maximum at every rotation. As a result, contact pressure of each tooth 4 with the cut material is gradually intensified/reduced at every rotation. That is, when a tooth 4a closest to the rotation axis C1 arrives at the cut material, contact pressure with the cut material is gradually reduced, and when a tooth 4b farthest from the rotation axis C1 arrives at the cut material, contact pressure is gradually intensified. The contact pressure of the tooth positioned at the tooth 4b part can thereby be heightened with small feed force, so that cutting resistance can be reduced.