A photosensitive member cartridge for use with an image-forming apparatus includes a photosensitive drum and a cartridge case comprising an upper wall, a bottom wall, a right side wall, and a left side wall. An outer surface of the upper wall faces upwards when the photosensitive member cartridge is installed in the image-forming apparatus. The right side wall extends upwardly from a right side of the bottom wall, and the left side wall extends upwardly from a left side of the bottom wall. The upper wall connects upper edges of the right side wall and the left side wall. A light-entrance portion is formed in the upper wall and is configured to allow a laser beam to pass through the upper wall and reach the photosensitive drum when the photosensitive member cartridge is installed in the image-forming apparatus.