An image forming apparatus includes a main body in which a photosensitive medium is disposed, and a developing device detachably disposed at the main body to develop electrostatic latent images on the photosensitive medium. The developing device includes a developing member disposed in a developing unit to supply developing agent to the photosensitive medium, a driven member to receive power from a driving member, and to allow the developing member to rotate, and a power transmitting member to connect the developing member and the driven member, and to absorb a movement of a normal force direction of a driving force generated between the driving member and the driven member.