Provided is a developing device configured to develop an electrostatic latent image formed on an image bearing member by feeding a toner to the electrostatic latent image. The developing device includes a developing frame configured to form an inner space in which the toner and a carrier are to be mixed, a developing roller including an outer periphery to which the developer attaches where the developing roller feeds the toner included in the developer to the image bearing member. The developing device includes an agitator installed in the inner space and configured to mix and deliver the toner and the carrier in a direction parallel to an axial direction of the developing roller, and a plurality of concave portions arranged on a bottom surface of the developing frame.