A developing device includes a developer bearer facing a latent image bearer, to rotate and supply developer to the latent image bearer, and a developer regulator to regulate an amount of the developer on a surface of the developer bearer. The developer regulator is in contact with the surface of the developer bearer. In the developing device, a ratio of a ten-point mean roughness of the developer regulator to a volume average particle diameter of the developer is not greater than 3.5%. The ratio is defined as Rzjis/Dv×100, where Rzjis represents the ten-point mean roughness measured in a nip-adjacent portion of a face of the developer regulator opposing the developer bearer, and Dv represents the volume average particle diameter of the developer. The nip-adjacent portion is adjacent to and downstream a downstream end of a regulation nip in a rotation direction of the developer bearer.