PURPOSE: To obtain a large-diameter lens with accurate curvature at low cost by fixing circumferential edges of two transparent flat plates to a holding member at a necessary interval, forming a transparent flat plate with charged liquid, and providing a support corresponding to necessary curvature outside of said transparent flat plate.

CONSTITUTION: The two transparent circular flat plates 1 and 2 are fixed to the holding member 3 in a liquid-tight state at their circumferential edge parts to form a space 4. When a lens is formed, transparent liquid 9 from a tank 10 is charged in the space 4 by a pump 6 through a pipe 5, and air bubbles are eliminated completely at the same time. When the pressure of the liquid 9 in the space is further raised by the pump 6, the flat plates 1 and 2 are curved to deform as shown by 1' and 2'. At this time, external surfaces of the curved plates 1' and 2' contact the insides of support parts 7c and 8c of supports 7 and 8; and the insides 7a and 8d of the support parts 7c and 8c are formed corresponding to a desired lens shape.