An image forming apparatus includes: a housing; a drum cartridge as a first cartridge including a photosensitive drum; a second cartridge accommodating toner; and a drawer movable between an inside position where the drawer in its entirety is positioned inside the housing and an outside position where at least a part of the drawer is positioned outside the housing. The drum cartridge is attachable to and detachable from the drawer. The drawer includes: a side plate configured to receive the photosensitive drum; and a locking member supported by the side plate. The locking member is movable relative to the side plate between a locking position where the locking member locks the photosensitive drum to the side plate and an unlocking position where the locking member unlocks the photosensitive drum from the side plate in an attached state of the drum cartridge to the drawer.