PURPOSE: To easily mold a large number of strain-free lenses in a short period of time by a method wherein ultraviolet-curing resin is poured in a matrix, the recessed bottom face of which is lens-like form, and, after that, ultraviolet rays are emitted under the condition that the exposure dose is regulated so as to be proportional to the wall thickness of the lens-like form in order to harden the ultraviolet-curing resin.

CONSTITUTION: In a matrix 1, in which a recess having the step-wise form of the desired Fresnel lens, liquid or gelatinous ultraviolet-curing resin 2 is poured so as to bond a transparent synthetic resin sheet 3 thereon. Next, from the synthetic resin sheet 3 side, ultraviolet rays are firstly spot-emitted to the center of the recess. Then, the irradiation range is gradually and concentrically enlarged so as to harden the ultraviolet-curing resin 2. Or the ultraviolet rays are, at first, emitted to the outer periphery of the recess. In succession, the irradiation may well be performed under the condition that the irradiation range is concentrically reduced toward the center of the recess. In the case of a lens, in which the farther the location becomes from the center, the thicker the wall thickness at the location becomes, such as a concave lens, the resin is hardened by emitting ultraviolet rays over ultraviolet-curing resin through a fan-shaped notch 10, which has its vertex at the center 9 of a rotary douser 8 and is rotated about its center 9. Or an ultraviolet spot irradiating source may well be rotated spirally and, at the same time, its rotating speed may well be regulated in proportion to the thickness of the lens in order to emit ultraviolet rays.