A tandem type of process unit removably loaded in an image forming device has a plurality of process cartridges, a pair of lower supporting plates, and a pair of upper supporting plates. Each of the plurality of process cartridges has a photosensitive drum rotatably about an axis extending in a first direction. Each of the plurality of process cartridges has two side faces facing each other in the first direction and a cartridge electrode provided on the side face. The plurality of process cartridges is aligned in a second direction perpendicular to the first direction. Each of the lower supporting plates supports a lower part of the side face of each of the plurality of process cartridges. The pair of upper supporting plates is positioned upward and separately from the pair of lower supporting plates. Each of the upper supporting plates supports an upper part of the side face of each of the plurality of process cartridges. The pair of upper support plates and the pair of lower support plates provide a side opening facing the side face of each of the plurality of process cartridges to expose the electrode of each of the plurality of process cartridges toward outside through the side opening.