PURPOSE: To form such a cutting portion as being yet thinner without entailing any drop in strength of a disc and make width of cut as well as to strengthen binding capacity in making the binding area increase, by making the wall thickness of a cutting portion forming part thinner than that of the disc, and forming a step part there.

CONSTITUTION: A lot of holes 3 are set up in random form in a cutting portion forming part 2 having proper width toward the center of a disc 1 from an outer circumferential end of the disc 1. Diamond fine grains 4 are bonded overall on a surface of this cutting portion forming part 2 and each inner circumferential wall of these holes 3, forming a cutting portion of a circular saw. At this time, wall thickness of the cutting portion forming part 2 is made thinner than that of the disc 1 except the cutting portion forming part 2, and a step part 6 is formed whereby binding force to the cutting portion forming part 2 of the cutting portion 5 can be strengthened. Along with this, stress to be received by these diamond fine grains 4 in and around this step part 6 can be held up with this step part 6, and the cutting portion 5, namely, the circular saw's durability is improvable. In addition, the yet thinner cutting portion 5 is formable without entailing any drop in strength of the disc 1 and, what is more, the width of cut can be smaller.