An image forming apparatus includes an image bearing member on which an electrostatic image is formed by imagewise exposure; a rotatable member; a developing device carried on said rotatable member and movable, by rotation of said rotatable member, to a developing position where said developing device is opposed to said image bearing member; a driven gear which is provided in said developing device and which receives a driving force for operating said developing device; and a driving gear, provided in a main assembly of the apparatus, for driving engagement with said driven gear of said developing device which is located at the developing position, wherein said driving gear, when said developing device is moving toward the developing position, is driven such that moving direction thereof is the same as a moving direction of said driven gear at an engagement portion with said driven gear, wherein upon driving engagement between said driven gear and said driving gear, a peripheral speed VA of said driven gear which is being moved by said rotatable member on an addendum circle thereof at said engagement portion and a peripheral speed VB of said driving gear on an addendum circle thereof satisfy 0.9≦VA/VB≦1.0.