Patent ID: 7756426

Claim:
An image forming apparatus comprising: an image forming apparatus body; a photosensitive unit removably mounted in the image forming apparatus body and having an image carrier; a developer cartridge which contains developer, the developer cartridge being removably mounted in the photosensitive unit and having a developer carrier; a driving unit provided in the image forming apparatus body; a drive member provided in the developer cartridge and permitted to be driven by the driving unit when the developer cartridge is mounted in the image forming apparatus body, consequently driven by a predetermined driving amount from start of the driving to end of the driving; a movement member which is movable with the driving of the drive member; a transmission member provided in the photosensitive unit and moved by abutment of the movement member against the transmission member; a detection unit provided in the image forming apparatus body for detecting the movement of the transmission member; and a information judging unit which judges information on the developer cartridge on the basis of a result of the detection by the detection unit, wherein the drive member is a partly toothed gear which includes a toothed portion to which a driving force from the driving unit is transmitted, and a non-toothed portion to which the driving force from the driving unit is not transmitted.