1. An image forming apparatus for forming images on a recording medium comprising: an electrophotographic printer engine for forming images having a plurality of colors; detection means for quantitatively detecting a state of devices of the image forming apparatus relating to image formation; control means for setting quantities of control for each color of said electrophotographic printer engine based on the detected state of each of the devices of the image forming apparatus; calculation means for determining, based on the quantities of state detected by said detection means, quantities of control using fuzzy sets, and for calculating quantities of control to be set by the control means for each color, each quantity of control corresponding to one of the detected quantities of state from a degree to which the quantity of state belongs to each fuzzy set; and an extraction means for extracting, in accordance with predetermined rules, a main quantity of control by which the control means sets the amount of each color in a specific position within the area represented by each quantity of control calculated by said calculation means.