A developer cartridge including a frame, a developer housing section, a developer supplying section, and at least one projecting portion is provided. The frame includes a first side wall, a second side wall, and a third side wall. The developer housing section houses a developer and the developer supplying section supplies the developer to a photosensitive member and houses a developer carrying member that extends in the width direction and is rotatably supported by the first side wall and the second side wall. The at least one projecting portion is located above the developer carrying member and extends from the frame beyond the back end substantially in the length direction, and the at least one projecting portion is provided integrally on the frame.