A color image forming apparatus including: a plurality of developing devices for forming a black toner image and a color toner image; an image carrier for carrying toner images; a density detecting device for detecting densities of the black toner image and the color toner image each on the image carrier, the density detecting device having a light emitting element and a light sensitive element; and a controller for the density detecting device; wherein, when detecting a density of the black toner image, the controller controls a drive voltage of the light emitting element so that an amount of received light from a non-image area becomes a first predetermined value; and when detecting a density of the color toner image, the controller controls the drive voltage so that an amount of received light from a non-image area becomes a second predetermined value.