To extend the life of a fly eye lens molding die to be used for molding a fly eye lens.

A lens molding recessed part 1 corresponding with each of a plurality of lens elements of the fly eye lens, is nicked in a fly eye work 8 which is a material of the fly eye lens molding die for molding the fly eye lens. In this case, the lens molding recessed part 1 is formed in the way that the ridge part 2 of a sharp edge shape generated in the border part between a plurality of the lens molding recessed parts 1, is rounded to the mutually different or equal curvature radius R1, curvature radius R2 and curvature radius 3. In the fly eye lens molding die thus obtained, the coating of the fly eye lens molding die can hardly come off and consequently, its life is extended.