A developing roller is located nearer a first end than a second end in a first direction. A first boss extends in a second direction and is movable together with a housing. The first boss bears the weight of a developer cartridge when the first boss is supported by a support surface of a first side plate of a drum unit, and is located away from the developing roller in the first direction and the third direction. A first pressure receiving surface is located farther away from the developing roller than the first boss in the third direction. The pressure receiving member receives a pressing force in the third direction from a pressing member of the first side plate of the drum unit. The first boss is located away from the developing roller in the first direction by a first distance. The first pressure receiving surface is located away from the developing roller in the first direction by the first distance or by a second distance smaller than the first distance.