A porous body containing a silicon component as a starting material of optical element is immersed in a solution containing hydrofluoric acid, taken out from the solution and immersed in a solution containing a metal alkoxide containing a first metal component except silicon or a derivative thereof so that the porous body contains the first metal component in such a concentration gradient that the concentration of the first metal component decreases from a periphery of the porous body toward a center of the porous body. Hydrofluoric acid breaks glass bonds of the porous body, so that the concentration of the first metal component can be securely distributed in a desired gradient. Drying and sintering of the porous body enables producing, for example, a glass having a metal component concentration concavely distributed in its radial direction which is excellent in chromatic aberration suppressing capability. After the immersion in the solution of first metal component, the porous body can be immersed in a solution of second metal component to thereby provide the porous body with a concentration gradient of second metal component.