A developing device that includes a developing member, a cylindrical layer thickness regulation member and a guide surface. The developing member retains a developer supplied from a developer accommodation portion and, while rotating, supplies the developer to an image-bearing body. The layer thickness regulation member comes up against the developer retained at the surface of the developing member and regulates a layer thickness of the developer. The guide surface guides developer that has been rendered excess by the layer thickness being regulated by the layer thickness regulation member toward the developer accommodation portion. The guide surface is provided such that an angle that is formed between the guide surface and a tangent of the layer thickness regulation member at a point of intersection of a line of extension of the guide surface with the layer thickness regulation member is at least 90°.