A belt tension adjustment mechanism provided on an inner side of an endless intermediate transfer belt and applying a tension to the intermediate transfer belt being rotated when a toner image is transferred on the intermediate transfer belt, said belt tension adjustment mechanism includes a holder having an opening section at one surface thereof; and an elastic member contained to be fixed in the holder while being compressed in a running direction of the intermediate transfer belt and having a convex section, wherein the convex section protrudes from the opening section of the holder toward a direction orthogonal to an image transfer surface of the intermediate transfer belt and is in direct contact with the intermediate transfer belt.