An optical device that has an antireflection function includes: a base; and a plurality of structural bodies, which are formed by convex portions or concave portions, arranged on a surface of the base with a fine pitch that is equal to or smaller than a wavelength of visible light. The plurality of structural bodies are arranged so as to form tracks of a plurality of rows on the surface of the base and form a quasi-hexagonal lattice pattern, a tetragonal lattice pattern, or a quasi-tetragonal lattice pattern, and a packing ratio of the structural bodies to the surface of the base is equal to or higher than 65%.