Patent ID: 7907855

Claim:
An image forming apparatus comprising: a first developing device including a first developer carrying member for carrying a developer containing toner, wherein a developing voltage including an AC component is applicable to said first developer carrying member to develop an electrostatic image; a second developing device including a second developer carrying member for carrying a developer containing toner, wherein a developing voltage including an AC component is applicable to said second developer carrying member to develop an electrostatic image; a transferring device for transferring a toner image formed by said first developing device to a moving transfer medium and then transferring a toner image formed by said second developing device onto the transfer medium; a controller for selectively executing an operation in a first mode wherein the image is formed by both of said first developing device and said second developing device or in a second mode wherein the image is formed by only said second developing device of said developing devices; and a bias controller for controlling an AC bias applied to said second developing device such that an amplitude of the AC bias applied to said second developing device in the first mode is smaller than the amplitude in the second mode.