A developing device includes a developer carrier to carry a developer, and a developer conveyor to supply the developer to the developer carrier. The developer conveyor includes a shaft extending in an axial direction to rotate in a rotational direction, a helical blade having a conveying surface to convey the developer around the shaft along the axial direction, and a protrusion attached to a rear surface of the helical blade, which faces the conveying surface, and having a leading surface extending from an upstream end to a downstream end in the rotational direction of the shaft.