An image forming apparatus forming an image in a plurality of colors (C, M, YL, K) comprising a reference color, the apparatus comprising: an image forming part for forming a first pattern image and a second pattern image, wherein elements of the first and second pattern images in the same color are arranged side by side in a main scanning direction, with respect to each of the plurality of colors; an intermediate transfer belt to which the first pattern image and the second pattern image formed by the image forming part are transferred, the intermediate transfer belt for conveying the transferred first pattern image and second pattern image in a sub-scanning direction; a first sensing unit for sensing an element of the first pattern image on the intermediate transfer belt; a second sensing unit for sensing an element of the second pattern image on the intermediate transfer belt; a location calculation unit for obtaining locations in the sub-scanning direction for the elements of the first pattern images and second pattern images of the plurality of colors on the intermediate transfer belt based on results of sensing performed by the first and second sensing units; and a control unit for obtaining rotational variance factors of the intermediate transfer belt for each of the plurality of colors based on the obtained locations for the elements of the second pattern image, correcting the obtained locations for the elements of the first pattern image using the rotational variance factor obtained from the second pattern image corresponding in color to the first pattern image, obtaining an offset of another color with respect to the reference color based on the location of the first pattern image after correction, and performing color registration based on the obtained offset to reduce the offset, wherein the first pattern image is an image for obtaining an offset of another color with respect to the reference color among the plurality of colors, and wherein the second pattern image is an image for obtaining a movement of the intermediate transfer belt in the sub-scanning direction. an image forming part for forming a first pattern image and a second pattern image, wherein elements of the first and second pattern images in the same color are arranged side by side in a main scanning direction, with respect to each of the plurality of colors; an intermediate transfer belt to which the first pattern image and the second pattern image formed by the image forming part are transferred, the intermediate transfer belt for conveying the transferred first pattern image and second pattern image in a sub-scanning direction; a first sensing unit for sensing an element of the first pattern image on the intermediate transfer belt; a second sensing unit for sensing an element of the second pattern image on the intermediate transfer belt; a location calculation unit for obtaining locations in the sub-scanning direction for the elements of the first pattern images and second pattern images of the plurality of colors on the intermediate transfer belt based on results of sensing performed by the first and second sensing units; and a control unit for obtaining rotational variance factors of the intermediate transfer belt for each of the plurality of colors based on the obtained locations for the elements of the second pattern image, correcting the obtained locations for the elements of the first pattern image using the rotational variance factor obtained from the second pattern image corresponding in color to the first pattern image, obtaining an offset of another color with respect to the reference color based on the location of the first pattern image after correction, and performing color registration based on the obtained offset to reduce the offset, wherein the first pattern image is an image for obtaining an offset of another color with respect to the reference color among the plurality of colors, and wherein the second pattern image is an image for obtaining a movement of the intermediate transfer belt in the sub-scanning direction.