Patent ID: 7962073

Claim:
An image forming apparatus comprising an image carrier for forming an electrostatic latent image on a surface thereof and a developing unit for developing the electrostatic latent image on said image carrier with a two-component developing agent, wherein the developing unit comprises: a developing agent carrier for developing the electrostatic latent image to form a visible image, wherein said developing agent carrier is disposed opposite to said image carrier with a gap; having inside thereof a development main magnetic pole for forming a bristle of a magnetic brush; and a plurality of magnetic poles for conveying the developing agent, wherein the developing unit performs a counter type contact developing method in which said image carrier and said developing agent carrier are moved in mutually opposite directions at a development area, the bristle of the magnetic brush is formed by the two-component developing agent on the surface of said developing agent carrier, and an alternating electric field having a DC component and an AC component superimposed on each other is used as a development bias applied to said developing agent carrier, and wherein, the development area is formed so that, a contact width of the bristle of the magnetic brush formed by said development main magnetic pole contacting on said image carrier is 70% or less with respect to a development width in which a toner on the surface of said developing agent carrier is transferred on to said image carrier, and a center position of the contact width is positioned on an upstream side with respect to a center position of the development width in a rotation direction of said image carrier.