also a multilaser having a plurality of light emitting points may be used as the light source in the present embodiment to thereby provide a multibeam scanning optical apparatus and it is possible to realize a color image forming apparatus which can highly minutely cope with a higher speed description will now be made of an image forming apparatus applied to the present invention fig9 is a cross sectional view of the essential portions of an embodiment of the image forming apparatus of the present invention in the sub scanning direction in fig9 the reference numeral 104 designates the image forming apparatus code data dc is inputted from an outside apparatus 117 such as a personal computer to this image forming apparatus 104 this code data dc is converted into image data dot data di by a printer controller 111 in the apparatus this image data di is inputted to an optical scanning unit 100 having the construction shown in embodiments 1 to 3 a light beam 103 modulated in conformity with the image data di is emitted from the optical scanning unit 100 and the photosensitive surface of a photosensitive drum 101 is scanned in the main scanning direction by this light beam 103 the photosensitive drum 101 which is an electrostatic latent image bearing member a photosensitive member is clockwisely rotated by a motor 115 with this rotation the photosensitive surface of the photosensitive drum 101 moves in the sub scanning direction orthogonal to the main scanning direction relative to the light beam 103 above the photosensitive drum 101 a charging roller 102 for uniformly.