Patent ID: 8086116

Claim:
An image forming apparatus comprising: a plurality of process cartridges, each of the process cartridges holding a photosensitive member on which an electrostatic latent image is configured to be formed, each of the process cartridges configured to develop the electrostatic latent image by supplying toner to the electrostatic latent image; an image forming unit which is configured to scan a laser beam in a main scanning direction to expose a respective one of the photosensitive members, and which is configured to form the electrostatic latent image on the respective one of the photosensitive members to form an image; a mirror that is provided on at least one of the process cartridges in a position lying within a range of an optical path of the laser beam for the one process cartridge and out of a range of an optical path of the laser beam for forming the electrostatic latent image on the photosensitive member of the one process cartridge, the mirror is provided for reflecting the laser beam; a first origin detection unit that is configured to detect the laser beam reflected by the mirror; and an optical path member that is provided in the process cartridges other than the process cartridge on which the mirror is provided, the optical path member extending from the mirror to the first origin detection unit when all the process cartridges are mounted in respective predetermined positions.