Patent ID: 7418215

Claim:
A developing device comprising: a developing housing that faces an image carrier on which an electrostatic latent image is carried and stores a developer which contains toner and magnetic carrier is housed in; a developer carrier that is disposed apart from the image carrier in the developing housing and carries and transports the developer; a developing bias applying unit that is disposed between the image carrier and the developer carrier and applies a developing bias for developing the electrostatic latent image on the image carrier, the developing bias comprising an AC component and a DC component, the AC component being superposed to the DC component; a volume resistivity detecting unit that detects a volume resistivity of the developer on the developer carrier; and a developing bias adjusting unit that sets the AC component of the developing bias to a reference value when the volume resistivity of the developer detected by the volume resistivity detecting unit falls within a given range, and corrects the AC component of the developing bias to cause an image quality evaluation parameter to fall within an allowable range when the volume resistivity of the developer exceeds the given range.