The image forming apparatus has an image forming device including a plurality of image forming units each having an image bearing member and attachable to and detachable from the image forming apparatus, and an intermediate transferring member disposed above the plurality of image forming units and bearing toner images transferred from the image bearing members of the image forming units, an opening portion, formed by rotating the intermediate transferring member upward, for attaching and detaching the image forming units, and a guide portion for guiding each of the image forming units to be attached and detached from the opening portion, wherein the guide portion for at least the image forming unit installed on the side of a rotating portion of the intermediate transferring member, is inclined in a direction opposite to the rotating portion. With this configuration, it is possible to prevent influence of an open/close cover when attaching and detaching a process cartridge.