Patent ID: 7480475

Claim:
A developing device for developing an electrostatic latent image formed on an image bearing member, comprising: a rotating developing roller bearing toner thereon, capable of developing the electrostatic latent image with the toner; a toner layer forming member configured to form a toner layer on the developing roller, and charge the toner of the toner layer at a nip between the developing roller and the toner layer forming member; and a toner supplying device configured to supply fresh toner to the developing device, wherein a charge quantity (q) of the toner on the developing roller varies according to the following equation: q ( t )= A·{ 1−exp(− t/t g )} (1) wherein t represents a nip passing time of the toner on the developing roller, t g represents a time constant of charging the toner, and A represents a constant, and wherein the time constant t g is smaller than a rotation time of the developing roller per rotation.