Patent ID: 6917780

Claim:
An image forming apparatus having at least one developing unit that develops an electrostatic latent image on a photosensitive body, the image forming apparatus comprising: a developing roll mounted in the developing unit; a magnetic roll mounted in the developing unit; a magnetic brush forming region on the magnetic roll; a toner thin layer forming region on the developing roll, wherein the toner thin layer forming region is smaller than the magnetic brush forming region; a high resistivity region adjacent each end of the toner thin layer forming region, the high resistivity region having resistivity higher than the toner; a developing bias applied to the developing roll, the developing bias having a first direct current bias and an alternating current bias; and a second direct current bias applied to the magnetic roll; wherein a difference between the first direct current bias and the second direct current bias at the time of a first revolution of the magnetic roll during the toner thin layer forming period is larger than the difference between the first direct current bias and the second direct current bias at a time of the second and subsequent revolution of the magnetic roll during the toner thin layer forming period.