Patent ID: 7742727

Claim:
An image forming apparatus, comprising: a photoconductive member on which a latent image is to be formed; a developing roller for developing the latent image formed on the photoconductive member by a first bias; a magnetic roller for forming a magnetic brush thereon with a two-component developer containing a carrier and a toner and forming a thin toner layer on the developing roller by a second bias; and a bias applying device for applying biases to the developing roller and the magnetic roller, wherein: the developing roller has a base body thereof made of aluminum and having a surface cleaned with an acid and treated with fluorine containing fine particles after being anodized in an acid aqueous solution and sealed in a nickel acetate solution; the first bias includes a first alternating-current bias in the form of a rectangular wave; and if T denotes the thickness of the thin toner layer and D 1 denotes the duty ratio of the first alternating-current bias, the thickness T and the duty ratio D 1 satisfy relationships of the following equations in the case of calculating the duty ratio D 1 using an application period of a voltage in a direction to transfer the toner from the developing roller toward the photoconductive member as a positive period: 7 μm≦T≦13 μm, and 35%≦D1≦70%.