An image forming apparatus for stabilizing image densities of a high-density image by devising shapes of test patches is provided. A test pattern image is created by adhering toner to a plurality of test patches having respectively different line area rates of 100% or less. An amount of adhering toner for a line area rate of 100% is calculated by detecting the amount of the toner adhering to the test pattern image. Then, process conditions are controlled so that the calculated amount of the adhering toner reaches a predetermined value. By doing so, the amount of the adhering toner of the high-density image is accurately controlled.