An image forming apparatus has an apparatus main assembly; an image forming unit; a fixing unit which has a pressure applying mechanism and a cam member; an opening and closing member which is attached to the apparatus main assembly to be capable of being opened and closed; a first gear which is provided at the apparatus main assembly; a second gear which is provided at the fixing unit; and a connection gear which connects the first gear and the second gear. The connection gear is configured to be detachable from between the first gear and the second gear and to be attachable being engaged with both the first gear and the second gear only in a case that the first gear and the second gear are respectively at a predetermined phase.