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 1 comprises a main body 2 and an image forming unit 30 removable from the main body 2. The main body 2 includes a gear 43 for receiving rotary driving force to the image forming unit 30 and a joint 45 and the image forming unit 30 has a coupling 36 for receiving rotary driving force from the main body 2. Furthermore, a joint holder section 43a for the gear 43 and the coupling 36 has a contact hole 47, and contact hole 36a, respectively and both ends of the joint 45 are inserted in those holes. The contact holes 47 and 36a are in not-twisted triangle pole shape and the joint 45 is in twisted triangle pole shape.