PURPOSE: To reduce the whole space of arrangement, by arranging a driving pulley and a drive pulley so that a part of them is overlapped each other, and putting the different projected parts of a belt having a plurality of projections on the driving pulley and the driven pulley respectively.

CONSTITUTION: A driving pulley 34 and a driven pulley 25 are arranged so that a part of them is overlapped each other in the axial direction, and the lower projection 38 of a belt 36 having integrally projections 37, 38 on the upper and lower sides thereof is put on the driving pulley 34, and the upper projection 37 thereof is put on the driven pulley 35. Thus, since the driving shaft 16 and the driven shaft 18 can be arranged so as to be adjacent to each other, the whole space of arrangement can be reduced.