A developing device includes developing units each including a first gear and a development roller; a rotation supporting member; a cam member having a cam surface surrounding the rotation axis, and being secured to 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 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 engagement of the first gear with the second gear before the first gear reaches the driving position.