an electrophotographic image forming apparatus usable with process cartridges . the apparatus includes mounting portions for detachably mounting the cartridges . in each mounting portion , a cartridge is inclined downwardly from an upstream to a downstream side with respect to a mounting direction and a phantom plane passing through axes of the drums is inclined toward a downstream side with respect to the mounting direction from a bottom part to a top part of the phantom plane . parts of cartridges mounted to a lower one and the next higher one of the mounting portions overlap , as seen along a plane perpendicular to the phantom plane from an upstream side with respect to the mounting direction . the apparatus also has a light projector and a feeder for feeding recording material , and the cartridges are mounted to or demounted from respective mounting portions from above the perpendicular plane .