Provided are a mask, a method of manufacturing the same, a light irradiation device, a method of radiating light, and a method of manufacturing an orientationally ordered photo-alignment layer. By the mask, collimated light or nearly collimated light may be irradiated with uniform illumination to a surface of an object to be irradiated. Further, by the mask, light may be effectively incident even on the object to be irradiated in the curved shape.