An image forming apparatus detachably mounts black and non-black cartridges each including a photosensitive drum and a developing roller. The apparatus includes a driving source; first and second clutches for connecting and disconnecting between the driving source and the developing roller of the black and non-black cartridges, respectively; movable first and second members actable on the first and second clutches, respectively, for switching between transmitting the driving force to the developing rollers and not transmitting the driving force; and a switching member, movable by the driving force of the driving source and actable on the first and second members for switching among first, second, and third modes for transmitting the driving force to the developing rollers of all of the cartridges, not transmitting the driving force to any one of the rollers, and transmitting the driving force only to the developing roller of the black cartridge.