Image forming apparatus, method of allowing driven member to be mounted on apparatus body in image forming apparatus and method of allowing drive force to be transmitted to belt unit in image forming apparatus

A method of allowing a driven member to be mounted on an apparatus body in an image forming apparatus having:

• the apparatus body that includes a drive source;
• the driven member that is detachably attachable to the apparatus body;
• a first transmission member that is provided in the apparatus body, that includes a base rotatable around a rotation axis, and that transmits drive force from the drive source to the driven member;
• and a second transmission member that is provided in the driven member, that includes a base rotatable around the rotation axis, and that transmits drive force from the first transmission member to the driven member, any one of the first transmission member and the second transmission member including a projection that projects from the base of the one of the transmission members, the other transmission member including a receiving port in the base of the other transmission member, the receiving port receiving the projection, the method of allowing the driven member to be mounted on the apparatus body in the image forming apparatus comprising:
• allowing the receiving port to receive the projection when a rotation angle between the second transmission member and the first transmission member is an angle set in advance and preventing the receiving port from receiving the projection when the rotation angle is out of the angle set in advance, at the time of mounting the driven member on the apparatus body,
• wherein the projection is singularly provided so as to be eccentric to the rotation axis, and the receiving port is singularly provided so as to be eccentric to the rotation axis.