To form a concave spherical face, of which the roundness value, surface accuracy, and pitch interval or the like are highly-accurate and uniform, on a molding face of a die by cutting work.

The concave spherical face 3 is formed on the molding face by applying fly-cut machining for cutting the molding face of the die 1 by scanning the central cross-section of the concave spherical face 3 while rotating a round-cutting tool 14, which has a cutting blade 16 with a curvature radius smaller than a curvature radius 18 of the concave spherical face 3, so that a rotational radius of the cutting blade 16 in the round-cutting tool 14 becomes the curvature radius 18 of the concave spherical face 3.