PURPOSE: To obtain a low aberration lens which does not require finishing to an aspherical surface, by cutting out a part having a necessary refractive index distribution from a base material glass plate provided with the refractive index distribution changing in the thickness direction from the surface toward the inside and finishing the same to a spherical surface.

CONSTITUTION: A base material glass plate 10 contg. cations contributing to an increase in the refractive index of glass such as Tl, Cs or the like is brought into contact with a medium 11 contg. ions contributing to a decrease in the refractive index of glass such as Na or K to substitute the ions in the part near the surface of the material 10 with the ions in the medium 11 thereby forming the refractive index distribution wherein refraction n (Z) is max. at the center of the thickness and decreases roughly parabolically toward both surfaces 10A of the plate and wherein the refractive index is uniform within the section parallel with the plane 10A of the plate, in the well thickness of the material 10. The high refractive index face side of the blank lens material 12 obtd. by cutting out the region of the necessary refractive index distribution from such material 10 is polished to a spherical surface with the Z direction normal to the plate plane of the material 10 as the optical axis of the lens and the low refractive index face side thereof is polished to the flat plane perpendicular to the optical axis.