A developing device is provided having a simple configuration by which a desired amount of developer can be delivered to an image bearing member, and there is provided an image forming apparatus having the developing device. The developing device includes a developing roller by which two-component developer is borne and delivered to a photoreceptor drum, a layer thickness-regulating member for regulating a layer thickness of the developer, and a magnetism-generating member for generating magnetism, and a control unit for controlling an amount of displacement of the magnetism-generating member.The control unit 23 controls an amount of displacement of the magnetism-generating member relative to the development sleeve.