An image forming apparatus which obtains rotational variance factors of an intermediate transfer belt for each of plurality of colors based on locations with respect to second pattern image being obtained by a location calculation unit, corrects the location obtained with respect to a first pattern image based on the rotational variance factor obtained with respect to the color of the first pattern image, obtains an offset of another color with respect to a reference color based on the location after correction, and performs color registration based on the obtained offset to reduce the offset.