A small color laser printer using four all-in-one cartridges has been developed. Four sector-shaped cartridges, each of which contains an OPC drum, a developing unit, a charger and a cleaner, are assembled into a rotary carousel. The carousel rotationally changes each color cartridge to produce primary color images which are superimposed onto an intermediate transfer belt to make a full-color image that is transferred to a paper all at once. This world-first color all-in-one cartridge eliminates hand-dirtying problems during toner and OPC replacement. Furthermore, fewer supply items and a 10,000-page long cartridge ensure less user intervention for the replacing of consumables. Its all-front-access structure which is similar to conventional monochrome lasers affords good user friendliness.