Patent ID: 8224217

Claim:
A developing unit to develop an image on an image support body, comprising: a housing to contain a developer having a toner and a carrier; a magnetic cylinder including a catch pole to pick up the developer in the housing and a main pole arranged to face the image support body and to hold the carrier of the developer; a sleeve installed to rotate on the magnetic cylinder and on which a developer layer is formed; a thickness regulating member to regulate a thickness of the developer layer; and a width regulating member to regulate a width of the developer layer on the sleeve to satisfy the following formula: W M ≧W D2 ≧W D1 ≧W Imax , where W M refers to a magnetization width of the magnetic cylinder, W D2 refers to a width of the developer layer at the catch pole, W D1 refers to a width of the developer layer between the catch pole or the thickness regulating member and a developing area formed between the sleeve and the image support body, and the W Imax refers to a maximum image width capable of being developed on the image support body.