An image forming apparatus according to an aspect of this invention includes: a photoconductive unit; an exposure unit outputting a pulse-width-modulated light signal and exposing the photoconductive unit; a developing unit developing the photoconductive unit and forming a developed image on the photoconductive unit; a transfer unit transferring the developed image to a transfer target unit and forming a transferred image; an image patch generating unit generating an image patch formed by a predetermined pattern; a sensor unit detecting density information of the developed image of the image patch formed on the photoconductive unit or the transferred image of the image patch formed on the transfer target unit; and an image quality maintenance control unit deciding a proper quantity of exposure and a proper pulse width on the basis of the density information detected by the sensor unit and set the decided proper quantity of exposure and the proper pulse width in the exposure unit.