In an image forming apparatus, a drum cartridge includes a photosensitive drum, a developing device, a drum cleaner, a waste toner tube, and a flange. The waste toner tube includes a first end portion communicating with the drum cleaner and a second end portion connected to the flange. The developing device includes a protruding portion facing the flange. The cushion member is located between the flange and the protruding portion. The cushion member allows a cartridge mounting part of the developing device to move with respect to the flange in a case where the developing device moves with respect to the photosensitive drum.