Patent ID: 6947692

Claim:
An image forming apparatus comprising: an image bearing member configured to bear an electrostatic latent image thereon; a developing sleeve comprising: a nonmagnetic sleeve having grooves with a depth of from 0.1 to 0.2 mm on an outer surface thereof in a longitudinal direction thereof at an interval of from 0.4 to 0.6 mm; and a magnet roller fixedly set in the nonmagnetic sleeve, wherein the developing sleeve magnetically bears thereon a magnetic two component developer comprising a toner and a carrier while rotating to form a magnet brush thereon, wherein the developing sleeve rubs the image bearing member with the magnet brush to visualize the electrostatic latent image at a rubbing region, wherein the magnet roller comprises a main magnet pole, which faces the latent image bearing member and which comprises a main magnet and auxiliary magnets adjacent to the main magnet, wherein the main magnet has a magnetic flux density in a normal line direction of from 100 to 200 mT at the rubbing region, an attenuation ratio of the magnetic flux not less than 40% and a half width not greater than 25°, and each of the auxiliary magnets has an attenuation ratio of a magnetic flux density in a normal line direction not less than 40%, and is arranged at an angle not greater than 35° from the main magnet, and wherein the toner has a volume average particle diameter of from 4.0 to 7.0 μm, and includes fine particles having a circle equivalent diameter not greater than 2 μm in an amount not greater than 20% by number.