Abstract: In an image forming apparatus and a controlling method thereof, the image forming apparatus comprises conveyer mechanisms for conveying collected toner to a waste part or a recycling part, and a controller for controlling the conveyer mechanism and a developer supplying device according to image forming conditions. When the image forming condition exceeds a predetermined reference level, the controller decreases a recycling rate of the collected toner. If the recycling rate becomes high as a result of the controlling, the controller decreases an amount of supplying the developer so as to lower toner density. Thus, reference toner density in the developer is controlled, thereby, high quality images can be maintained, and the controller can be simplified.

Abstract: The present invention, for example, forms a test pattern image on the surface of a photosensitive member at predetermined periodicity and detects the density of said test pattern image. If the detected density value of the test pattern image is other than said target value, the charging voltage is preferentially adjusted to maintain a stable toner density. When the adjusted charging voltage attains either an upper limit or a lower limit, the toner density is adjusted.