An image forming apparatus forms decision registration mark for deciding whether or not a color registration correction for correcting color shifts in the color image carries out on an intermediate transfer belt. The decision registration mark is formed by registering four color registration marks. Color registration sensors detect a detection width of the decision registration mark along a sub scanning direction. A control portion receives the detection width of the decision registration mark and decides whether or not the color registration correction carries out based on whether or not the detection width of the decision mark detected by the detection portion exceeds the period of reference time. When the detection width of the decision mark detected by the detection portion exceeds the period of reference time, the control portion carries out the color registration correction.