A technique enabling downsizing of an image forming apparatus is provided. A cleaning unit 13 attachable to and detachable from an apparatus main body of an image forming apparatus 100 that forms an image on a recording material 12 is provided, with this cleaning unit 13 including: a photosensitive drum 1; and a cleaning frame body 14 that supports the photosensitive drum 1 and that includes an opening 14c through which laser light 3c for exposing the photosensitive drum 1 can pass, wherein the opening 14c is configured such that a width of the opening 14c in a scanning direction in an irradiation range of the light for exposing the photosensitive drum 1 becomes greater toward a side of the photosensitive drum 1 from a side of a light source of light for exposing the photosensitive drum 1.