PROBLEM TO BE SOLVED: To solve the problems in a conventional transmission gear of a waste culm cutter in which a driving belt of a combine cutter is bridged for an interval long in the longitudinal direction from a first spiral shaft of a threshing device to a rear end cutter shaft, therefore the side edge of the belt comes into sliding contact to easily cause friction damage of the belt, however the problems are difficult to cope with the adjustment by line alignment and the change of a pulley width, and the maintenance is complex.SOLUTION: A counter pulley 18 for fitting and rotationally guiding a V-shaped face of a cutter drive belt 17 is provided in the front end of a side wall part 9 of a waste culm cutter 6. There are provided a tension pulley 19 for bringing an outer circumferential surface of the cutter drive belt 17 area bridged between this counter pulley 18 and a rear side cutter shaft pulley 16 into tension swinging, and a tension V pulley 23 integrally rotated with the tension pulley 19. The tension pulley 19 and the tension V pulley 23 are swung, and the cutter drive belt 17 and a diffusion interlock belt 22 are brought into tension, and thereby the transmission of a cutter shaft 15 and a diffusion shaft 20 is performed.
