Patent ID: 7362990

Claim:
An image forming apparatus, comprising: an image bearing member; a latent image forming device to form an electrostatic latent image on said image bearing member; a magnetic field generating device to generate a magnetic field to be applied onto both a developer bearing member and said image bearing member; and a developing device to develop said electrostatic latent image so as to form a toner image on said image bearing member; wherein, at a developing region, said developer bearing member moves in a direction opposite to a moving direction of said image bearing member and said magnetic field generating device has a developing pole to form a magnetic brush for developing said electrostatic latent image; and wherein an outer diameter of said developer bearing member and a magnetic flux density of said developing pole fulfill the relationship indicated as follow: Br 1≧ R× 4.5 where Br 1 (mT): magnetic flux density of said developing pole, R (mm): outer diameter of said developer bearing member.