The present invention provides a cartridge which is dismountable from the main assembly without deteriorating usability performance in a predetermined direction substantially perpendicular to the rotational axis of an image bearing member, the main assembly being not provided with the mechanism for moving the main assembly side engaging portion in the rotational axis direction in response to the opening and closing operation of the main assembly cover of the main assembly.With the movement of the cartridge in such a direction perpendicular to the rotational axis of the image bearing member in the dismounting of the cartridge from the main assembly of the electrophotographic image forming apparatus, the coupling member movable in a direction parallel with the rotational axis of the image bearing member enters a inside of a recess of the main assembly side engaging portion provided in the main assembly of the apparatus to receive a rotational force from the main assembly side engaging portion.