A developing device for an image forming apparatus and capable of maintaining desirable image quality by reducing a change in the charged state of the surface of a developing roller and a change in the amount of charge to deposit on a developer. An insulating layer constitutes the surface of the developing roller and is made of a material more than 50 percent of which constitutes a non-polar high molecule. This prevents a toner from filming the surface of the roller. The insulating layer is implemented by a material substantially the same as the toner in charge series, so that the toner is frictionally charged by a member other than the developing roller. A discharge brush is held in contact with the roller and made of a material substantially identical with the toner in charge series, thereby preventing the toner from being frictionally charged by the brush even when the toner films the roller. Further, the insulating layer is constituted by a material in which a non-polar high molecule and a polar high molecule are mixed in a suitable ratio. As a result, a space charge is scarcely stored in the surface of the roller, thereby preventing a charge from being injected into the roller surface.