| 摘要 |
A developing unit which forms an image on a photosensitive medium, includes a housing which accommodates a developer, a magnetic cylinder having a catch pole which picks up the developer in the housing by a magnetic force, and a main pole which couples a carrier among the picked-up developer, a sleeve rotatably installed on a circumference of the magnetic cylinder to form a magnetic brush having a predetermined width on the circumference by the developer picked up by the catch pole, and a sealing member provided at opposite end parts in an axial direction of the sleeve to prevent a leak of the developer, wherein a width Ws of the sleeve, a magnetized width WM of the main pole, a magnetized width Wc of the catch pole, and a width WB of the magnetic brush satisfy WS>WM>WB>WC.
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