Patent ID: 6901233

Claim:
A developing unit comprising: a developing device including a magnetic pole for forming a magnet brush on a surface of a developer carrier; and an image carrier facing said developing carrier and carrying a latent image to be developed by said magnet brush on a surface of said image carrier; wherein assuming that a dark portion has a potential of V D , a potential after exposure is V L , and a bias for development is V B , then there holds a relation: 0 <|V D |−|V B |<|V D −V L |<400 V assuming that, in a relation of image density to a development potential in a range stated above, a maximum slope [ΔID/Δ(V B −V L )max] and a slope at a maximum value of V B −V L [ΔID/Δ((V B −V L )MAX)] are A and B, respectively, then there holds a relation: 0.9 ×A>B and an attenuation ratio of the magnetic pole in a developing region in a normal direction is 40% or above.