An image forming apparatus includes a transport unit comprising a transport belt which transports a printing medium in a transport direction along a transport path, an image forming unit which transfers toner to the printing medium to form an image, a density evaluation unit which is provided on the transport path of the transport belt and evaluates a density of the image formed by the image forming unit, and a controller which controls the image forming unit to form a test image which has a length in a transport direction that is determined by a position deflection of the transport belt, controls a characteristic of the image forming unit based on a density evaluation of the test image, and controls the transport unit to make the transporting speed of the transport belt a predetermined value or less during the density evaluation of the test image by the density evaluation unit.