An image forming apparatus, comprising: a plurality of cartridges which are configured to be detachabley attached to a main body of the image forming apparatus in a direction to come apart from a rotation axis of an image bearing member at image forming status, each of the plurality of cartridges comprising at least an image bearing member for bearing an electrostatic image, development means for developing the electrostatic image on the image bearing member with a developer, and transfer means for transferring the developer image developed by the development means from the image bearing member onto a transfer medium in a transfer section, a plurality of developer accommodation vessels disposed in correspondence to the plurality of cartridges to accommodate replenishing developers, wherein the plurality of developer accommodation vessels are disposed at places which do not overlap moving ranges of the plurality of cartridges in detaching and attaching processes, supplying means for supplying developers in the developer accommodation vessels to the development means, driving means for offering driving power to the cartridges, cleaning means for cleaning developer on the image bearing member, and waste developer collection vessels for containing developer removed by the cleaning means, wherein at least one of the transfer sections of the plurality of cartridges is located at a different position in a vertical direction with respect to the positions of the other transfer sections; and wherein the capacity of the developer accommodation vessel corresponding to the cartridge whose transfer section is located at a vertically lowest position is larger than those of the developer accommodation vessels of the cartridges whose transfer sections are disposed vertically upward of the transfer section located at the vertically lowest position, characterized in that the cartridges are disposed in a main body frame of the image forming apparatus, both the developer accommodation vessels and the waste developer collection vessels are disposed outside of the main body frame of the image forming apparatus at the same side, and the driving means is disposed outside of the main body frame of the image forming apparatus at a different side from the developer accommodation vessels. a plurality of cartridges which are configured to be detachabley attached to a main body of the image forming apparatus in a direction to come apart from a rotation axis of an image bearing member at image forming status, each of the plurality of cartridges comprising at least an image bearing member for bearing an electrostatic image, development means for developing the electrostatic image on the image bearing member with a developer, and transfer means for transferring the developer image developed by the development means from the image bearing member onto a transfer medium in a transfer section, a plurality of developer accommodation vessels disposed in correspondence to the plurality of cartridges to accommodate replenishing developers, wherein the plurality of developer accommodation vessels are disposed at places which do not overlap moving ranges of the plurality of cartridges in detaching and attaching processes, supplying means for supplying developers in the developer accommodation vessels to the development means, driving means for offering driving power to the cartridges, cleaning means for cleaning developer on the image bearing member, and waste developer collection vessels for containing developer removed by the cleaning means, wherein at least one of the transfer sections of the plurality of cartridges is located at a different position in a vertical direction with respect to the positions of the other transfer sections; and wherein the capacity of the developer accommodation vessel corresponding to the cartridge whose transfer section is located at a vertically lowest position is larger than those of the developer accommodation vessels of the cartridges whose transfer sections are disposed vertically upward of the transfer section located at the vertically lowest position, characterized in that the cartridges are disposed in a main body frame of the image forming apparatus, both the developer accommodation vessels and the waste developer collection vessels are disposed outside of the main body frame of the image forming apparatus at the same side, and the driving means is disposed outside of the main body frame of the image forming apparatus at a different side from the developer accommodation vessels.