Image forming apparatus with a removable process unit capable of securing rotation transmission accuracy without stressing a holding portion despite shaft misalignment

a aa It is intended to provide an image forming apparatus capable of securing rotation transmission accuracy among input/output axes without giving stress to a holding portion despite shaft misalignment and without using material of high strength. A color printer comprises a main body and an image forming unit removable from the main body . The main body includes a gear for receiving rotary driving force to the image forming unit and a joint and the image forming unit has a coupling for receiving rotary driving force from the main body . Furthermore, a joint holder section for the gear and the coupling has a contact hole , and contact hole , respectively and both ends of the joint are inserted in those holes. The contact holes and are in not-twisted triangle pole shape and the joint is in twisted triangle pole shape.