An image forming apparatus is provided with a device for forming an electrostatic image on an image bearing member. A developer develops a latent image formed on the image bearing member and includes a developing unit having a developer carrying member for carrying thereon and supplying a developer to the image bearing member. A moving member moves the developing unit between an operative position and a non-operative position away therefrom. A supporting member supports the developing unit for rotation about an axis, the supporting member rotatably supporting the developing unit at one side and supporting the developing unit at the other side for rotation and movement in a predetermined direction. An urging device urges the developing unit toward the image bearing member adjacent the other side, and a driver applies a driving force to the developer carrying member of the developing unit. When the developing unit is rotated about the axis and moved to the operating position by the moving member, and the driver is operated, the developing unit is urged toward image bearing member about the axis. The developer has a plurality of such developing units.