PURPOSE: To provide a combine harvester capable of performing operations while automatically preventing defective threshing from occurring even when any of stems and culms having long and short culms are reaped.

CONSTITUTION: This combine harvester is capable of regulating a dust feeding valve 40a to an opening and a closing sides in a threshing chamber with an electric motor M, making the dust feeding valve 40a guide and act on threshing treated materials helically transferred to the rear end side of a threshing cylinder by rotation of the threshing cylinder 33, changing the helical transfer direction and thereby changing the time for the threshing treated materials to stay in the threshing chamber. When the first reaping and pretreating device 10 for harvesting short culms capable of cutting planted stand stem and culms at plant feet and feeding the whole reaped stems and culms to the threshing chamber is replaced with the second reaping and pretreating device 20 for harvesting long culms capable of reaping the planted stand stems and culms at the plant feet and feeding only parts of ear tip sides in the reaped stems and culms to the threshing chamber, the electric motor M is automatically operated based on sensed results whether either of the first reaping and pretreating device 10 and the second reaping and pretreating device 20 is connected. Thereby, the dust feeding valve 40a is automatically regulated to the opening and closing sides.