A developer cartridge including a frame, a developer housing section, a developer supplying section, a developer electrode, and an input gear 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 housing section, for housing a developer, extends from the first side wall to the second side wall in a width direction substantially perpendicular to the length direction. The developer supplying section, for supplying the developer to a photosensitive member, extends from the first side wall to the second side wall in the width direction and houses a developer carrying member. The developer carrying member includes a developer carrying member shaft and a developer carrying member body that is supported on the developer carrying member shaft. The developer carrying member shaft extends in the width direction and is rotatably supported by the first side wall and the second side wall. The developer electrode electrically biases the developer carrying member, and at least a portion of the developer electrode is connected to the first side wall and the developer carrying member. The input gear supplies a driving force for rotating the developer carrying member.