PURPOSE: To prevent an optical element from deformation, crack and occurrence of foam in burning process even in the case of enlarging refractive index difference and diameter.

CONSTITUTION: In producing a refractive index distribution type optical element by a sol-gel method, a process for providing a distribution to the skeleton density in a gel and another process for providing a concentration distribution in the direction opposite to this skeleton density distribution are provided. As shown as the figure (a), the density distribution in the direction opposite to distribution of refractive index is previously given to the skeleton structure of silicone which is a cage and concentration distribution of a metal component for providing the distribution of refractive index is given to the skeleton. Thereby, the distribution of porosity and shrinkage amount in the radial direction are nearly uniformed as shown in the figures (b) and (c).