The method for producing an image forming apparatus includes emitting light beams from a printhead; optionally irradiating a photoreceptor with the light beams to form a latent image; optionally forming a visible image on a recording medium corresponding the latent image; obtaining plural pieces of information concerning a property of the light beams or lightness of the visible image at different positions in a direction; calculating variation width of N pieces of information corresponding to an attention area having a predetermined length in the direction; determining the number of pieces of information used for subjecting each of the N pieces of information to moving averaging, based on the variation width; when the number is two or more, subjecting each of the N pieces of information to moving averaging; and correcting quantities of light beams corresponding to the N pieces of information based on the average values.