Developing unit and image forming apparatus using the same

A developing unit comprising:

• a development housing with an opening for development formed therein in such a manner as to oppose a latent image carrier,
• a developer carrier disposed in face-to-face relation to said opening for development, and
• two-component developer having a magnetic carrier and a toner is carried on a surface of said developer carrier, so as to convert an electrostatic latent image on said latent image carrier into a visible image in a development region opposing said latent image carrier of said developer carrier, wherein
• said developer carrier comprises:
• a development sleeve for carrying the two-component developer and disposed rotatably so as to rotate from an upper side toward a lower side in the development region, and
• a magnet member which is fixedly provided inside said development sleeve and in a periphery of which a plurality of magnetic poles are arranged, and
• said magnet member comprises:
• a development magnetic pole disposed at a position corresponding to the development region and contributing to development,
• a pickup magnetic pole disposed in a region which is located on a lower side than the height of a rotational center of said development sleeve in a region where said development sleeve in terms of its rotating direction is headed from the lower side toward the upper side, and adapted to capture the developer inside said development housing onto a surface of said development sleeve, and
• a trimming magnetic pole disposed on a downstream side, in the rotating direction of said development sleeve, of said pickup magnetic pole and adapted to cause a portion of the developer captured by said pickup magnetic pole to drop.