A cartridge attachable/detachable to/from a main assembly of an image forming apparatus, the cartridge includes a developer storage unit configured to store developer, a partitioning member movably provided inside the developer storage unit and configured to partition the developer storage unit, a developer conveyance member configured to convey the developer stored in the developer storage unit, and an operated portion configured to move the partitioning member, wherein when the cartridge is attached to the main assembly, the operated portion is moved by touching the main assembly to move the partitioning member from a first position to a second position where the developer storage unit is caused to be greater in capacity than that in the first position.