An optical device includes a concave-convex structure layer having a concavo-convex structure on a surface thereof, the concavo-convex structure formed of a plurality of convexities or a plurality of concavities which are arranged with a sub-wavelength period, a high refractive index layer made of a material having a refractive index higher than that of the concavo-convex structure layer and located on the concavo-convex structure while having a surface conforming to the concavo-convex structure, and a low refractive index layer made of a material having a refractive index lower than that of the high refractive index layer and located on the high refractive index layer. The high refractive layer includes first grating high refractive index portions located at a bottom of the concavo-convex structure to form a first sub-wavelength grating, and second grating high refractive index portions located at a top of the concavo-convex structure to form a second sub-wavelength grating.