Patent ID: 8660461

Claim:
An image forming apparatus comprising: a body; a drum shaft attached to the body; a drum unit, which includes a photoreceptor drum with a hollow portion formed in an axial center thereof, configured to be attachable to and detachable from the body through inserting the drum shaft into the hollow portion of the photoreceptor drum; a plurality of ribs that is formed on the drum unit along an attaching and detaching direction of the drum unit with respect to the body; a guide rail, which is formed in the body, configured to allow the drum unit to slide when the plurality of ribs is placed on the guide rail; and a plurality of cutouts formed in the guide rail, the plurality of cutouts being engaged with the plurality of ribs when the drum unit is positioned at a regular position in the body after completion of attaching the drum unit to the body, and lengths of the plurality of cutouts being configured to be greater in increasing order from upstream to downstream of a direction in which the drum unit is inserted into the body; wherein the drum shaft and the guide rail are configured with respect to each other such that a center of the drum shaft is substantially coaxial with a center of the photoreceptor drum when the drum unit slides relative to the body in a state in which the plurality of ribs is placed on the guide rail.