a multi - beam image forming apparatus includes a beam generating unit 101 , an optical scanner 102 , an image processing unit 103 for dividing image data into several areas in a primary scanning direction , and image writing units 106 and 107 for writing an image while switching multiple laser beams in accordance with each of the areas in the primary scanning direction in a printing region based on the divided image data , wherein the image processing unit 103 judges continuity of the image data when dividing the image data , so that the image processing unit 103 divides the image data at an image data portion having continuity and transmits the divided image data to the image writing units 106 and 107 . the multi - beam image forming apparatus is provided as an apparatus in which scan positions can be aligned accurately both in the primary scanning direction and the secondary scanning direction and which is suitable for wide printing .