A developer cartridge includes a housing for accommodating developer, a rotation shaft rotatably supported by the housing and passing across an inside of the housing, a supply opening formed in a wall of the housing opposite in a diameter direction of the rotation shaft, a return opening formed in the wall of the housing at a position displaced from the supply opening in an axial direction of the rotation shaft, a first agitation blade supported by the rotation shaft and passing through a position opposite the return opening along an inner surface of the housing, and a second agitation blade supported by the rotation shaft and passing through a position opposite the supply opening along an inner surface of the housing, wherein the first agitation blade is configured to allow the developer returned through the return opening to flow into the housing.