PURPOSE: To produce easily a distributed index medium having the refractive index changing stepwise in the optical axis direction and a low aberration by laminating plural planar media having the refractive indices different from each other in order of the refractive indices.

CONSTITUTION: Plural optical planar glass plates 1 having the refractive indices different from each other are prepd. The plates 1 are laminated in order of the refractive indices by adhesion or melt-sticking and are made thinner by heating and stretching if necessary. The intended distributed index medium 2 having the refractive indices changing stepwise in the optical axis direction is obtd. The production of the medium 2 is also possible by supplying a gaseous raw material for forming glass to a burner for synthesizing fine glass particles, forming the fine particles for forming glass consisting essentially of SiO2 and contg. a dopant to adjust the refractive indices by a flame hydrolysis method and sticking and growing the fine particles on the substrate from the direction perpendicular thereto while changing the concn. of the dopant then vitrifying the particles.