PURPOSE: To enable the simple changeover from a state in which cut culms from a threshing waste culm cutter are collectively discharged into a narrow range to a state in which the cut culms are diffused and discharged into a wide range.

CONSTITUTION: The structure for threshing and treating waste culms of a combine harvester is obtained by securing and fixing the first guide plate 26 in a cut culm discharge port 25 of a threshing waste culm cutter so as to enable the rocking operation of the second to the fourth discharging guide plates 27 to 29 by sliding operation of one posture changeover tool 30. When the posture changeover tool 30 is operated to a diffusing position where a corner part 30b coincides with a diffusion display mark 31a, all the intervals D1, D2 and D3 of the first to the fourth discharge guide plates 26 to 29 are enlarged toward the downstream side of the cut culm flow direction. When the posture changeover tool 30 is operated to a position where the corner part 30b coincides with a collection display mark 31b, all the intervals D1, D2 and D3 of the first to the fourth guide plates 26 to 29 are narrowed toward the downstream side of the cut culm flow direction.