To provide a novel technique for producing a difference in refractive index between two regions. An optical element according to the present invention includes a first porous region (2002), a second porous region (2004), and a non-porous region (2003) formed between the first porous region (2002) and the second porous region (2004), the non-porous region having a refractive index higher than a refractive index of the first porous region.