IMAGE DENSITY ADJUSTING METHOD

PURPOSE:To maintain stable images which are small in environmental variation for a long period as any image by detecting the toner content in a developer and correcting the developing electric field of an image part on an image carrier according to the toner detection signal. CONSTITUTION:A reflection type density sensor 10 which is arranged nearby opposite a photosensitive body 1 detects a reference image formed on the photosensitive body 1 outside the image are and the supply amount of the developer is varied according to the density detection signal; and a toner density sensor (magnetic permeability sensor) 11 provided in a developing unit 4 is utilized to the toner concentration in the developer, thereby correcting and controlling the developing electric field at the image part. Consequently, the stable image is obtained as any of a solid image, a line image and a do image for along period even if the surface potential of an image carrier varies owing to environmental variation or a secular change.