An image forming apparatus includes a plurality of image forming parts, a moving medium continuously moving on the image forming parts, first and second image forming devices, a test image density measuring device, and a control device. The first test image forming device forms a first test image on the medium by using the image forming parts in a first order. The second test image forming device forms a second test image on the medium. The control device controls image forming processing in the image forming parts based on a result of a density measurement of the second test image.