To provide a lens having a refractive index distribution and low coefficient of thermal expansion.

A flat plate-shaped lens 103 includes: multiple kinds of polymerization of organic monomers; and a transparent material 101 whose refractive index distribution is formed by the multiple polymerization and in which particles having a coefficient of thermal expansion lower than that of the transparent material, are dispersed. The coefficient of thermal expansion of the lens is lower than that of the transparent material itself since the particles having a coefficient of thermal expansion lower than that of the transparent material are dispersed. Therefore, the lens is less deformed even when being heated.