Patent ID: 8498556

Claim:
A developing device comprising: a plurality of developing units each including a first gear that receives driving force and a development roller that rotates by the driving force received by the first gear; a rotation supporting member that is supported by a base so as to be rotatable around a rotation axis, the rotation supporting member supporting the developing units around the rotation axis, the rotation of the rotation supporting member causing the developing units to revolve around the rotation axis; a cam member having a cam surface surrounding the rotation axis, the cam member being secured to the rotation supporting member and rotating together with the rotation supporting member; and a driving force transmission member including a cam receiving roller and a second gear, the cam receiving roller being biased towards the cam surface while being supported by the base so as to be changeable between to contact and separate from the cam surface, the biasing pushing the cam receiving roller against the cam surface, the second gear being biased along with the cam receiving roller, the second gear engaging the first gear of the developing unit among the developing units whose development roller is moved to a position opposing an image carrying member by the rotation of the rotation supporting member, and transmitting the driving force to the first gear to develop a latent image on the image carrying member, wherein the cam surface includes a curved surface whose curvature is less than a curvature of the cam receiving roller so that, as the first gear approaches a driving position where the first gear receives the driving force from the second gear by the rotation of the cam member, the cam receiving roller is moved away from the rotation axis once, after which the cam receiving roller is moved towards the rotation axis, thereby starting the engagement of the first gear with the second gear before the first gear reaches the driving position.