An image forming apparatus includes a toner image forming device configured to form a toner image on an image conveying member, a detector configured to optically detect a density of the toner image on the image conveying member, a controller configured to control an image forming condition of the toner image forming device based on an output of the detector, a shutter configured to open and close an optical window of the detector, wherein the image forming apparatus is operable in a cleaning mode of the shutter in which an opening and closing movement of the shutter is repeatedly executed.