Abstract: A plate-like rotary body such as a circular saw has zigzag slits formed in the outer peripheral area or spanning the outer and middle peripheral areas such that the resulting protruding sections on both sides of each slit are elongated and deformed within its plane so as to touch the adjacent protruding section from opposite side, thereby providing frictional resistance to suppress vibrations of the body when it rotates. Such slits are preferably formed by a high-energy beam such as a laser beam or an electron beam for efficiency.