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.