A developing device includes a developer bearing member that bears a developer on its surface to supply the developer to an image bearing member having a first dielectric portion and a second dielectric portion in its surface, a regulating member that regulates a thickness of a layer of the developer carried by the developer bearing member, and a flexible sheet-like charging auxiliary member disposed so as to be in contact with the developer bearing member at a position downstream of a contact portion between the developer bearing member and the image bearing member and upstream of a contact portion between the developer bearing member and the regulating member in a rotational direction of the developer bearing member, where the charging auxiliary member charges the developer carried by the developer bearing member. In a triboelectric series, the charging auxiliary member is positioned between the first and second dielectric portions.