A developing device, an image forming apparatus, and an image forming system with which it is possible to appropriately perform developing operations are achieved. A developing device attachable to and detachable from a body of an image forming apparatus, is provided with: a developer bearing roller for bearing a developer; a first driving wheel that is provided on an end of the developer bearing roller and that is for driving the developer bearing roller; a second driving wheel that, in a state where the developing device is attached to the body of the image forming apparatus, receives a drive force from the body of the image forming apparatus and that transmits the drive force to the first driving wheel; and a positioning member that is made of metal and that is for positioning the first driving wheel and the second driving wheel.