Patent ID: 8026940

Claim:
An image forming apparatus that forms a color image through the steps of forming latent images by applying laser beams to photosensitive drums via polygon mirrors for a predetermined number of colors that is two or more, forming toner images corresponding to the formed latent images, and superposing the toner images of the predetermined number of colors to be transferred to a paper sheet, the image forming apparatus comprising: a number of polygon driving portions, equal to the predetermined number, that drive a number of polygon mirrors, equal to the predetermined number, to rotate at preset steady-state rotation frequencies; a number of beam detecting portions, equal to the predetermined number, that detect laser beams scanning by the predetermined number of polygon mirrors at preset positions on scanning paths; a reference phase setting portion that sets a substantially intermediate phase between a most leading phase and a most lagging phase among rotation phases of the predetermined number of polygon mirrors as a reference phase that is a phase to be a reference of the rotation phases of the predetermined number of polygon mirrors based on a result of detection by the predetermined number of beam detecting portions; and a phase control portion that controls the polygon driving portions so that rotation phases of the predetermined number of polygon mirrors match the reference phase.