An image forming apparatus has a speed range showing image forming capability per unit time that is determined in advance, and is settable to either a model set at a relatively low-speed range or a model set at a relatively high-speed range. Then, the arrangement of the laser elements is differentiated between a low-speed machine and a high-speed machine each other. Even when timing of writing for the high-speed machine is applied to the arrangement of the laser elements for the low-speed machine to write in an image, the image is not able to be written successfully, and resulting in an image which is displaced vertically.