To smoothly supply developer to a developing device from the beginning by actively breaking an agglomeration of developer in a developer supply container, especially near a developer discharge opening.

In the developer supply container having at least a developer storage section storing developer and the developer discharge opening through which the developer is discharged, each end of the developer storage section is extended within the main body of an image forming apparatus when the developer supply container is attached to the main body of the developing device disposed in the image forming apparatus. The developer discharge opening is unsealed accompanying the operation of increasing the capacity of the developer storage section.