In a tandem type image forming apparatus of this invention provided with image forming units arranged under an intermediate transfer medium and further, an exposure device arranged under the image forming units, developing devices are arranged so that exposure positions of image carriers and developing rollers come to the opposite sides with toner stirring mixers put between them. Further, there are guides extending under cleaning blades below the cleaning blades to receive falling toners. Further, suction ducts are provided to suck in the air around the developing devices. A slit area formed by the guides and an area of a laser beam projecting unit of the exposure device are arranged while they are shifted. Formed images are exposed at a sufficient exposure light intensity by preventing the laser beam injection unit of the exposure device from being stained and a toner image of high quality is obtained.