A method of easily manufacturing a light diffusion film by a continuous process, which achieves both good display properties and an increase in viewing angle when used in a liquid crystal display. A method of manufacturing a light diffusion film includes forming a laminate of an original light diffusion film and a photosensitive resin, wherein the photosensitive resin includes at least two types of materials that are different in refractive index from each other; and irradiating the laminate with a collimated laser beam from a side of the original light diffusion film, wherein a reflection hologram formation-preventing layer is located on a side of the laminate opposite from the side of irradiation of the laminate with a collimated laser beam. In the process of irradiating the laminate, the reflection hologram formation-preventing layer prevents formation of a reflection hologram on the photosensitive resin due to a reflected light from the irradiation.