A developing unit and an image forming apparatus having the developing unit are disclosed. The developing unit includes a developing unit main body having a supporting groove that contacts and is supported by the supporting protrusion of a frame when the developing unit is mounted on the mounting frame. A photoconductor is rotatably disposed in the developing unit main body and has ends that form a supporting shaft and are supported by a supporting unit. A driven unit is disposed in the developing unit main body and geared with the driving unit when the developing unit main body is mounted on the mounting frame. One of side surfaces of the developing unit main body includes an interference unit that interferes with the mounting frame and push the developing unit main body into engagement with the driving gear when the developing main body is mounted on the mounting frame.