The invention has an image forming apparatus with a deviation amount calculator for obtaining, by an arithmetic operation, by an arithmetic operation, the deviation amount between the laser beam irradiating positions for each color, under the condition that the deviation amount increases gradually according to a time lapse in at least one of the plurality of operating modes, according with a further time lapse, the deviation amount between the laser beam irradiating positions for each color decreases gradually, and according with a further time lapse, the deviation amount between the laser beam irradiating positions for each color is converged.