In a mill having a first mill provided with a first grinding surface and a second mill provided with a second grinding surface, the first grinding surface includes a first groove in a curved shape which extends from a side of a center of rotation C toward an outer circumference, the second grinding surface includes a second groove in a curved shape which extends from the side of the center of rotation C toward the outer circumference, and while the first grinding surface and the second grinding surface are superimposed on each other, the first groove and the second groove are not superimposed on each other and an angle (an angle of intersection) β at which the first groove and the second groove intersect with each other is 10°≤β≤50°.