A developer supply cartridge supplies a developer into a process
cartridge, and is detachably mountable to a main assembly of an
electrophotographic image forming apparatus. The process cartridge
includes a drum, a developing roller, a receiving-side shutter portion
opening and closing a developer receiving opening, a receiving-side
movable portion to move the receiving-side shutter portion, and a
regulating member for regulating movement of the receiving-side movable
portion. The developer supply cartridge includes a supplying-side
developer accommodating portion, a developer supply opening supplying the
developer from the supplying-side developer accommodating portion into
the process cartridge through the developer receiving opening, a
supplying-side shutter portion opening and closing the developer supply
opening, and a supplying-side movable portion to open the supplying-side
shutter portion when the developer supply cartridge enters the main
assembly and the process cartridge is set in the main assembly, by
engagement with the receiving-side movable portion.