An image forming apparatus includes a main body casing; a first drum unit including a first photosensitive drum configured to rotate about an axis extending in a first direction; a second drum unit including a second photosensitive drum configured to rotate about an axis extending in the first direction; a belt; a cleaning member configured to clean the belt; an auger configured to convey waste toner cleaned by the cleaning member; a first toner cartridge including a first new toner containing unit configured to supply new toner and a waste toner containing unit configured to contain the waste toner conveyed by the auger; and a second toner cartridge including a second new toner containing unit configured to supply new toner to the second drum unit. The waste toner containing unit is aligned with the first new toner containing unit in a second direction perpendicular to the first direction.