An image forming device including a casing having a front wall formed with a first opening and an upper wall continuous to the front wall and formed with a second opening. The first and second openings together form a single opening. The device further includes a door for covering the single opening, a belt unit, and a guide member. The belt unit includes first and second rollers, and a conveyer belt. The drawer is configured to accommodate a plurality of cartridges. The guide member is configured to movably guide the drawer. The first roller is disposed nearer to the single opening than the second roller to the single opening. In a state where the door is opened and the drawer is inside the casing, one of the plurality of cartridges closest to the door is detachably attachable to the drawer through the single opening.