1. An image forming apparatus comprising: a plurality of sequentially arranged image carriers; a conveying belt which conveys a print medium onto which color-separated images formed on the plurality of image carriers are overlapped; and a plurality of image transfer rollers installed to respectively correspond to the plurality of image carriers with the conveying belt being interposed between the image transfer rollers and the image carriers, wherein at least one of the plurality of image transfer rollers is arranged to be compressed with a pressure higher than those applied to the other image transfer rollers against the plurality of image carriers.