An image forming apparatus is described. The image forming apparatus may include an image forming apparatus body and a photosensitive unit detachably mountable to the image forming apparatus body. The photosensitive unit includes: a frame; photosensitive bodies supported by the frame; cartridges including a developer carrier and detachably mountable to the frame; and a pressing portion provided on the frame for pressing the cartridges to direct the developer carrier toward the corresponding photosensitive body. Each cartridge can shift in the frame to a first attitude pressed by the pressing portion, and a second attitude released from the press of the pressing portion and detachable from the frame. The image forming apparatus body is provided with an abutment portion abutting the cartridge in the second attitude thereby bringing the cartridge into the first attitude when the photosensitive unit is mounted to the image forming apparatus body.