Patent ID: 7664439

Claim:
An image forming apparatus, comprising: an image bearer configured to bear an electrostatic latent image on the surface thereof; a magnetic field generator configured to generate a magnetic field; a developer bearer comprising a non-magnetic developing sleeve, configured to rotate and bear at least one two-component developer comprising a magnetic carrier and a toner; a developing electric field generator configured to generate a developing electric field between the image bearer and the developer bearer; and an image developer configured to agitate the magnetic carrier and the toner to form two-component developer and develop the electrostatic latent image therewith in the developing electric field to form a toner image, wherein the two-component developer at least has a current speed index (25FRI) of from 0 to 2.0, which is determined by the following formula: 25 FRI =(total energy at 10 mm/s/total energy at 100 mm/s) wherein the total energy is an integral sum of a rotary torque and a vertical load when a blade of a powder fluidity analyzer spirally rotates at 10 mm/s and 100 mm/s, respectively, in the developer having a volume of 25 ml after idly agitated in the image developer for 10 minutes.