To provide a means for easily supplying a metallic endless belt to a belt device installed in a wide range and mounting it.

In the method of manufacturing the endless belt, by a dedicated working apparatus, the first wide surface 2 of a belt material is polished except for non-polished parts 3 and 4 of both ends to form a polished part P of a predetermined polishing amount. Then, the belt material is wound around a bobbin to be transported from the working apparatus to the arrangement place of a belt device. In the arrangement place of the belt device, the belt material 1 is wound around the drum of the belt device so that both ends are positioned in a lower belt traveling position. Then, parts of the respective non-polished parts 3 and 4 are cut so that the length of the belt material 2 in a belt longitudinal direction is equal to a predetermined belt effective length, and then both ends are welded to form the belt material 1 into an endless belt. Then, a part other than the polished part P of the first wide surface 2 of the endless belt is polished so that its polishing amount is equal to that of the polished part P.