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.