Patent ID: 8774680

Claim:
An image forming apparatus comprising: a plurality of image bearing members configured to be electrically charged at surfaces thereof; a plurality of exposing units configured to expose the electrically charged surfaces of said image bearing members to light and thus form electrostatic latent images; a plurality of developing units configured to attach developers to the electrostatic latent images to thereby form visible images; an intermediate transfer unit to which the visible images formed on the surfaces of said plurality of image bearing members are transferred; a first rotatably driving unit configured to rotatably drive, among said plurality of image bearing members, a first image bearing member used in a monochrome mode and said intermediate transfer unit; a second rotatably driving unit configured to rotatably drive, among said plurality of image bearing members, second image bearing members other than the first image bearing member used in the monochrome mode; a phase detecting unit configured to detect phases of rotation of said plurality of image bearing members; and a control unit configured to control the phases of rotation of said plurality of image bearing members based on the detection results of said phase detecting unit, wherein said control unit controls, in performing image formation in the monochrome mode, said first rotatably driving unit and said second rotatably driving unit so that a rotational speed of said second rotatably driving unit is slower than a rotational speed of said first rotatably driving unit without adjusting the phases of rotation of said plurality of image bearing members, while driving both the first and second rotatably driving units.