To provide a diamond tool by which a molded face with high accuracy can be molded, a machining method, and a molding metal mold and an optical element manufactured thereby, in manufacturing the molding metal mold for molding a ring zone lens in which a boundary portion between a circular face and an adjacent ring zone and a boundary portion between respective adjacent ring zones are connected with a fine step portion having the circular face for centering the axis of light and at least a piece of the ring zone represented by a diffractive lens, for instance.

The molded face with high accuracy can be molded into a mold while avoiding the risk of breakage in manufacturing the molding metal mold for molding the ring zone lens, for instance, since a cutting edge is provided with a first edge portion 3b in a straight state, a second edge portion 3c extending and existing in the crossing direction with the first edge portion 3b and a rake face 3a profiled by a circular arc portion 3d connecting the end in the first edge portion 3b with the end in the second edge portion 3c, when the radius of the circular arc portion 3d is made to be r (μm), the 0.05≤r≤2.5 is satisfied in the diamond tool 3 retaining the cutting edge comprising diamond on a shank.