A developing device including a developer bearing member rotatable while bearing developer on a surface thereof, a rotary body having a rotary shaft, a casing that contains the developer supplied to the surface of the developer bearing member to accommodate at least a portion of the rotary body, a rotary gear having a rotary shaft parallel to the rotary shaft of the rotary body and disposed outside a lateral wall of the casing to support an end of the rotary shaft of the rotary body, and a stationary shaft member fixed to the lateral wall of the casing to rotatably support the rotary gear. An axial center of the stationary shaft member is collinear with an axial center of the rotary shaft of the rotary body.