A photoreceptor cartridge unit having a cartridge frame made of plastic on which a photoreceptor drum acting as a rotary member and its peripheral components are integrally mounted. The cartridge frame is formed with a plurality of bearing portions for supporting the rotary members and a plurality of positioning projections and is split, at the bearing portions, into two frame portions provided with an engageable portion and a receiver portion, respectively. The peripheral components are formed with a plurality of positioning holes so as to be mounted on the cartridge frame through engagement of the positioning projections with the positioning holes. The two frame portions are coupled with each other through engagement of the engageable portion with the receiver portion.