Patent ID: 7941080

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 first bias includes a first alternating-current bias in the form of a rectangular wave and the second bias includes a second alternating-current bias in the form of a rectangular wave; and if D 1 denotes the duty ratio of the first alternating-current bias and D 2 denotes the duty ratio of the second alternating-current bias, the duty ratios D 1 , D 2 satisfy the following relationship when the duty ratio D 1 is calculated 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 and the duty ratio D 2 is calculated using an application period of a voltage in a direction to transfer the toner from the magnetic roller toward the developing roller as a positive period: D 1>100− D 2.