A developer regulating member regulates a thickness of a layer of a developer on a surface of a developer bearing body. The developer has a degree of circularity in a range from 0.94 to 0.97. The developer regulating member includes a resilient plate member composed of a metal material and having a bent portion. An outer surface of the bent portion contacts the surface of the developer bearing body so that a ridge line of the outer surface of the bent portion crosses a moving direction of the surface of the developer bearing body. A curvature radius R (μm) of the outer surface of the bent portion and a mean crystal grain diameter D (μm) of the metal material satisfy the relationship: 60×10−3×R−11≦D≦93.75×10−3×R−6.875.