The invention relates to a developer cartridge for exchanging developers in an apparatus which develops an electrostatic latent image, and an image forming apparatus using the developer cartridge. The developer cartridge has a first storage room for unused developer, a second storage room under the first room for storing used developer, openings in the first and second rooms and shutters provided therewith, together with a paddling mechanism in the first storage room for moving unused developer. The image forming apparatus has an endless latent carrier, a mechanism for forming an electrostatic latent image on the carrier and a mechanism for developing the latent image on the carrier. The developer cartridge is detachable positioned to the developing mechanism and a mechanism is provided for driving the shutters of the developer cartridge for exchanging used developer with unused developer.