Abstract: A belt member of the present invention includes ribs that prevent the belt member from being shifted to either side. A plurality of cuts are formed in each rib at preselected intervals in the circumferential direction of the belt member, and each extends from the top toward the bottom of the rib. The cuts may be replaced with projections and recesses alternating with each other in the cicumferential direction of the belt member or bores formed at preselected intervals in the above direction. Such ribs allow, without being subject to a heavy load, the belt member to be wrapped around a support roller with a large curvature or bent in the inverse direction. This reduces deterioration and slippage ascribable to the position of the belt member desirable for the size reduction of an apparatus on which the belt member is mounted.