PURPOSE: To lengthen a lifetime by forming a slot extended in the direction of a shaft at a position different from a notch section along the circumferential direction of a blade and at a position where a distance from the nose of the blade to an end section on the nose side of the slot is brought to the notch depth or less of the notch section, in the blade.

CONSTITUTION: A plurality of slots 1f extended along the direction of a shaft are shaped along the circumferential direction of a diamond blade 1a in the intermediate section of the blade 1a. The slots 1f are formed at positions different from notch sections 1e along the circumferential direction and at locations where distances 100f from the nose of the blade 1a to end sections on the nose sides of the slots 1f are brought to the notch depth 100e of the notch sections 1e. When the cutting and dressing of a semiconductor substrate are repeated, the notch sections 1e are reduced gradually, but one ends of the slots 1f are cloven in place of the reduction of the notch sections 1e, and novel notch sections are formed. Accordingly, when the blade is wasted, slots as the novel notches are shaped in place of the notch sections, thus allowing the longer maintenance of the grinding capacity of a core drill, then improving profitability.