Patent ID: 7412190

Claim:
A developing apparatus in which a magnetic brush is formed by magnetically applying a two-component developer, which is constituted by at least a magnetic carrier and a negatively charged toner comprising toner particles and an external additive, onto a developer carrier, and an electrostatic latent image formed on a latent image carrier is made visible by said magnetic brush, said developing apparatus comprising: stirring means for stirring and dispersing said developer and conveying said developer to a predetermined position within a developing container; and toner replenishing means for replenishing toner that is consumed during development, wherein an area in which a relationship of 0.6<Vlocal/Vaverage<0.9, where Vaverage is an average flow speed of said developer during one circuit of said developing container and Vlocal is a local flow speed of said developer as said developer moves through said developing container, is satisfied exists in said developing container, and said negatively charged toner maintains a relationship of μ 0 (t)≧μ 1 (t) between an electrostatic charge distribution peak position μ 0 (t) of toner in an external force imparting developer and an electrostatic charge distribution peak position μ 1 (t) of said replenishing toner, said relationship being measured in a deteriorated toner testing method.