A developer cartridge including a frame, a developer supplying section, a developer housing section, and an extension portion is provided. The frame includes a first side wall and a second side wall, and the first side wall and the second side wall extend substantially in a length direction. The developer supplying section supplies a developer to a photosensitive body cartridge, and the developer supplying section extends in a width direction substantially perpendicular to the length direction from the first side wall to the second side wall. The developer housing section houses the developer, and the developer housing section extends in the width direction between the first side wall and the second side wall. The developer housing section includes an open end at which the developer housing section adjoins the developer supplying section, and a closed end opposite from the open end. The closed end includes an exterior surface extending from a substantially bottommost portion of the developer housing section to a top portion of the developer housing section. The extension portion includes a first extension portion that extends away from the developer housing section in a first direction substantially perpendicular to the width direction and a second extension portion that extends away from the first extension portion in a second direction different from the first direction.