A driving motor for a color black is shared between a photosensitive body for the color black and a driving roller that drives an intermediate transfer belt not shown. Furthermore, a driving motor for colors yellow, magenta, and cyan is shared between photosensitive bodies for the colors yellow, magenta, and cyan. Driving of the driving motor for the colors yellow, magenta, and cyan is controlled based on a first waveform as a speed fluctuation waveform of the photosensitive body for the color black obtained when the driving motor for the color black is driven at a predetermined speed and second waveforms as speed fluctuation waveforms of the photosensitive bodies for the colors yellow, magenta, and cyan obtained when the driving motor for the colors yellow, magenta, and cyan is driven at a predetermined speed.