PURPOSE: To maintain cutting ability at a constant level until an ultra-hard grinding grain is extinguished by exposing the top of a tooth board formed in great number on a periphery of a base, and by adhering the ultra-hard grinding grain to the remainder of the tooth board surface.

CONSTITUTION: On a periphery of a disc-shaped base 6 of 0.35-0.55mm in thickness, a great number of trapezoid tooth boards 7 are formed along the circumference, while the width of each tooth board 7 in a circumferential direction is defined approximately two times as thick as that of the base 6. Outer face of the top or tooth part 5 of each tooth board 7 being exposed, an ultra-hard grinding grain 8 is adhered to the remainder of the base 7 surface. At the time of cutting, as the outer face of the tooth part 5 of the tooth board 7 and the ultra-hard grinding grain 8 adhered to the periphery come into contact with a work, respectively, the grinding grain 8 mainly cutting the work, the tooth part 5 is abrased through the contact with the work. When the grinding grain 8 is extinguished by the abrasion an ultra-hard grinding grain 8 situated on a basic side of a next step comes into contact with the work, and the cutting is continued.