An image forming apparatus has a tray, which is able to be drawn out of the apparatus and on which a plurality of cartridges of different sizes can be mounted. A cartridge, being the largest in size among a plurality of process cartridges, is detachably arranged at a location at which it is first exposed to outside when a cartridge tray is drawn out. A developer storage portion of the largest cartridge has the largest capacity and stores a developer of a black color.