A developing unit to develop an image on an image support body and an image forming apparatus employing the same. The developing unit includes 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.