PURPOSE: To prevent a belt from coming off from its proper track and finally from a pulley by coaxially installing an O-ring having a larger diameter than the outer periphery of said belt at the pulley part, to said pulley for driving or supporting a conveying belt, additionally to said belt set around said pulley and the other pulley.

CONSTITUTION: An endless belt 2 set around a pair of pulleys 4, 5, is rotated by driving a motor 1, to convey a wafer 7 from a left end toward right. And, when the wafer 7 is positioned on an O-ring 3 provided on the pulley 5 on the right end, the wafer 7 is continuously supported by two points of a point P on the belt 2 and a point Q on the O-ring 3 and conveyed in the direction of B. In this case, even if the wafer 7 may rotate from some cause or other, since the parts of the belt 2 and the O-ring 3 which are brought into point contact with the wafer 7, are rolled around the pulley coming off from the wafer 7, the belt 2 is not affected by the rotation of the wafer 7, without getting off its track and without being removed from the pulley 2.