A charger and a developing roller are disposed substantially in a line on both sides of a photosensitive drum in a cross sectional view in a direction perpendicular to an axis of the photosensitive drum, so that no process device is disposed on an upper portion of the photosensitive drum. Thus, a scanner unit can be disposed close to the photosensitive drum. Further, as the photosensitive drum is wide open at its upper portion, a range of a laser beam emitted from the scanner unit is widely provided. Accordingly, parts making up the scanner unit can be arranged with great flexibility, thus the scanner unit can be made thin. Thereby, the laser printer can be made thin.