An optical diffusion film comprises a plurality of diffraction grating cells formed on a substrate, each cell comprising a plurality of curved gratings disposed in parallel with each other and containing the same profile. Such film can be manufactured by embossing, using an original plate formed by etching a photosensitive material by means of an electronic beam exposure system to produce gratings. When such a film is provided with a reflection layer and exposed to light coming obliquely from above, highly bright and diffracted light is emitted in a predetermined direction.