PURPOSE: To obtain a stable visible image without soiling in the background, by providing a developer flow control board in the place where the developer is held by the magnetic brush roll and starts to flow from the developing region again to the developing container, and producing a uniform staying of the developer.

CONSTITUTION: The gap between a magnetic brush roll 3 and a photosensitive drum 1 is set wider than the gap between the magnetic brush roll 3 and a trimmer 7. In the downstream of the developing region where the photosensitive drum 1 and magnetic brush roll 3 approach each other, that is, in the place where the developer is held on the magnetic brush roll 3 and starts to flow from the developing region again into the developing container, a developer flow control board 6 is provided, while keeping contact with the ear of the developer brush, in the entire region in the axial direction of the magnetic brush roll 3. As a result, a uniform staying of the developer may be produced, so that the magnetic brush developer does not directly collide against the photoreceptor on the flow-in side of the developer. Hence, a stable visible image without soiling in the background may be obtained.