A process unit has process cartridges, a pair of lower supporting plates, and a pair of upper supporting plates. Each process cartridge has a photosensitive drum rotatably about an axis extending in a first direction. Each of the process cartridges has two side faces facing each other in the first direction and a cartridge electrode provided on the side face. The process cartridges are aligned in a second direction perpendicular to the first direction. Each lower supporting plate supports a lower part of the side face of each process cartridge. Each upper supporting plate supports an upper part of the side face of each process cartridge. The pair of upper support plates and the pair of lower support plates provide a side opening facing the side face of each process cartridge to expose the electrode of each process cartridge toward outside through the side opening.