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. Also, the cartridge includes a supply opening formed in a wall of the housing opposite in a diameter direction of the rotation shaft, and a return opening formed in a wall of the housing at a position displaced from the supply opening in an axial direction of the rotation shaft. In addition, the cartridge includes 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 from above to below the position opposite the return opening along with a rotation of the rotation shaft, 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.