An electrophotographic image forming apparatus for forming an image on a recording material, to which a process cartridge is detachably mountable, the apparatus, includes (a) a plurality of mounting portions for detachably mounting process cartridges, respectively, the process cartridges each including, an electrophotographic photosensitive drum, a developing roller for developing an electrostatic latent image formed on the electrophotographic photosensitive drum, a developer accommodating portion for accommodating a developer for use by the developing roller to develop the electrostatic latent image, a developer supply opening for supplying the developer to the developing roller from the developer accommodating portion, a sealing member for unsealably sealing the developer supply opening, and unsealing means for unsealing the developer supply opening by removing the sealing member from the developer supply opening; (b) a motor; and (c) driving force transmitting means for selectively transmitting a driving force from the motor to the unsealing means to unseal the developer supply openings of the process cartridges mounted to the mounting portions.