An image drum cartridge includes supporting walls, on which a photoconductive drum rotates, a position selector, a developing roller that rotates relative to the position selector, a developing blade that forms a thin layer of toner on the developing roller, and a slideable member that urges the developing blade against the developing roller. The position selector is mounted on the supporting walls and movable between first and second positions. The position selector causes the developing roller to move to an operative position where a nip is formed between the photoconductive drum and the developing roller. The position selector causes the developing roller to move to an inoperative position where no nip is formed between the photoconductive drum and the developing roller. The developing roller has a first rotational axis and the position selector has a second rotational axis away from the first rotational axis.