A transmitting diffraction element may include a transparent substrate, and a plurality of convex parts periodically formed on one surface of the transparent substrate, and be configured to diffract incident light to the transparent substrate. Each of the convex parts may include first, second, third, and fourth layers that are stacked on the transparent substrate. The first and third layers may be made of a material having a high refractive index, and the second and fourth layers may be made of a material having a low refractive index that is lower than the high refractive index.