At least one exemplary embodiment is directed to an optical unit adapted to irradiate image exposure light to an image carrier comprises a frame containing optical parts arranged therein and having an opening, and a cover adapted to cover the opening. The cover can be fixed by fixing members to the frame at three points in a first plane including the opening. The cover can further be fixed by fixing members to the frame at a second plane positioned on the frame and being adjacent to the first plane and at a third plane positioned on the frame and being not parallel to the second plane. Thus, an optical unit can be obtained which has high rigidity while, when the cover is attached to the opening, maintaining satisfactory flatness of the cover in a plane including the opening.