1. An image formation apparatus, wherein an electrostatic latent image is formed on an image supporting object, which electrostatic latent image is developed with a toner, the image formation apparatus comprising: a developing unit; a toner supply unit for supplying the toner to the developing unit; a patch image density detecting unit for detecting density of a patch image formed on the image supporting object; a toner density detecting unit for detecting density of the toner held in the developing unit; and a control unit connected to the patch image density detecting unit and the toner density detecting unit on an input side of the control unit, and connected to the toner supply unit on an output side of the control unit; wherein the control unit is capable of adjusting a generating interval of the patch image according to a detection result of the patch image density detecting unit so that the image density value may become equal to a predetermined target density value.