An image forming apparatus includes a display panel, a sheet conveying passage, a reading unit, a light source, a chassis, and a controller. The reading unit includes a light transmitting plate and a conveying image sensor. The conveying image sensor reads a conveyed sheet, which is a sheet to print on. The chassis has a cleaning hole in which to insert a cleaning rod for rubbing the light-transmitting plate. In a maintenance mode, the controller turns on the light source, and makes the display panel display a graph showing the pixel values of the pixels included in conveyed-and-read image data acquired by reading with the conveying image sensor.