To provide an end mill with an edge of diamond or a cubic crystal boron nitride.

At least a pair of spiral grooves 18 are provided on a rotary cutter blank 12. In the grooves 18, a polycrystal powder diamond or a powder cubic crystal boron nitride is filled and sintered. The angle of the groove is selected to form a positive or a negative rake angle when necessary, and then, a recess form flute 14 having the edge end parallel to the edge end 15 of the polycrystal diamond filled in the groove of the blank 12 is formed neighboring the respective grooves. By grinding a diamond in such a condition, the diamond loss is extremely little, and the perfect condition of a cutter is never hurt.