A dynamic pressure in the coolant supplied between a rotating grinding wheel and a rotating workpiece is released by making at least one of oblique grooves on the grinding wheel pass vertically through a contact surface on which a grinding surface of the grinding wheel contacts the workpiece. Where one and the other side intersection points are defined as intersection points at which both ends of each oblique groove respectively cross extension lines of one and the other side edges parallel to a grinding wheel circumferential direction of the contact surface, the other side intersection point of each oblique groove overlaps the one side intersection point of an oblique groove next to each such oblique groove by a predetermined overlap amount in the grinding wheel circumferential direction, and the length in the grinding wheel circumferential direction of the contact surface is made to be shorter than the overlap amount.