Patent ID: 8755702

Claim:
An image forming apparatus, comprising: an exposure portion to expose a surface of an image carrier to form an electrostatic latent image; a developing device which includes an agitating roller to agitate a developer, a developing roller to transfer toner of the developer on a surface of the image carrier and a toner concentration sensor to detect a toner concentration, said developing device developing the electrostatic latent image formed on the image carrier to form a toner image; a drive source to independently drive to rotate the developing roller and the agitating roller; and a control unit to control the drive source to change a rotational frequency of at least one of the developing roller and the agitating roller according to the toner concentration detected by the toner concentration sensor, wherein when the toner concentration detected by the toner concentration sensor is not more than a first threshold value, the control unit rotates the developing roller at a first rotational frequency, and rotates the agitating roller at a second rotational frequency which is larger than the first rotational frequency.