Patent ID: 6941090

Claim:
A developing apparatus for developing a latent image on a latent image carrying member with a magnetic brush made of developer comprising toner and magnetic carrier, comprising: a developer carrying member being rotated in a state where said magnetic brush is being formed thereon so as to develop said latent image; a first permanent magnet being built in said developer carrying member at a fixed position facing said latent image carrying member, said first permanent magnet serving as a main pole and generating a magnetic field of said main pole so as to form a first magnetic brush of the developer on said developer carrying member; a developing unit casing covering said developer carrying member, said developing unit casing having an aperture to expose said developer carrying member at the position facing said latent image carrying member; and a second permanent magnet being built in said developer carrying member at a fixed position near said aperture at a downstream side from said first permanent magnet with respect to a rotational direction of said developer carrying member, said second permanent magnet serving as an auxiliary pole and generating a magnetic field of said auxiliary pole so as to form a second magnetic brush of the developer on said developer carrying member, wherein said developing unit casing has a concave structure to form a low pressure area at a position facing said second permanent magnet, and said concave structure is concave toward an extension of said second magnetic brush so as to have a larger gap there between said developer carrying member and said developing unit casing than a gap at a tip part of said aperture between said developer carrying member and said latent image carrying member.