An image forming apparatus includes a transfer member configured to receive an image, and a first image forming unit including a first image bearing member and a first pair of developing units having developers of colors different from each other, and a second image forming unit including a second image bearing member and a second pair of developing units having developers of colors different from each other and from the first pair of developing units, each of the first and second image forming units configured to slidably move in a direction parallel to a horizontal plane of the image forming apparatus in a manner facing a surface of the transfer member and to be biased toward a desired position with respect to the transfer member when a cover of the image forming apparatus is moved to its closed position.