A plurality of process cartridges are detachably mountable to an electrophotographic image forming apparatus along a substantially vertical line. The cartridges each have an electrophotographic photosensitive drum, process means actable on the drum, and a drum shutter movable between first and second positions. The apparatus includes mounting portions for detachably mounting the cartridges, an opening for permitting passage of the cartridges into the apparatus, a covering member for covering the opening, and a pressing member for moving the shutter to the second position thereof when the covering member moves from an open position to a closed position. An angle of rotation of the shutter rotated from the first to the second position in the bottommost cartridge is larger than an angle of rotation of the shutter rotated from the first position to the second position in another one of said process cartridges.