A developing roller and a photosensitive drum are aligned in a second direction different from a first direction. A toner storage portion stores toner to be supplied to the photosensitive drum by the developing roller. A waste-toner storage portion stores toner conveyed through a conveyance pipe. The waste-toner storage portion has a main portion and a protruding portion protruding from the main portion in the first direction. A drum cartridge has a guide portion configured to guide the protruding portion of the waste-toner storage portion when a developing cartridge is being mounted on the drum cartridge. The guide portion includes first and second guides. The first guide extends in a third direction different from the first and second directions. The second guide continues from the first guide and is located closer to the photosensitive drum than the first guide is. The second guide extends in the second direction.