Provided are a developer cartridge and a developing apparatus using the developer cartridge, the developer cartridge making it possible to set the amount of developers that can be received to be large even when used in a miniaturized developing device and simplify the mechanism for opening/closing a supply outlet of the developer cartridge. As a result, the developer cartridge has no wasted space and thus can be miniaturized. In order to attain the above, the present invention provides a developer cartridge including a developer receiving portion that receives a new developer and has a section formed to have a shape that occupies a substantially entire space that is allocated to the developer cartridge to be attached.