In an image forming apparatus a forming unit forms an image using a light color toner and a dark color toner having the same hue as the light color toner. A patch image is formed with the light color toner and the dark color toner, and has different image density level portions. In the patch image, a difference in image density levels between adjacent image density level portions in a transition range before and after a switching region between a range in which either one of the light color toner or the dark color toner is used and a range in which both of the light color toner and the dark color toner are used is smaller than a difference in image density levels in the other ranges. Densities of the patch image are detected and the image density is controlled in accordance with a detected output.