PURPOSE: To provide a device capable of exhibiting satisfactory performances in response to wide working conditions on a dust-discharging treatment.

CONSTITUTION: The characteristic of this dust-discharging and treating device in a thresher comprises extending a dust-discharging and treating chamber to the end part of the frame, the dust-discharging and treating chamber being disposed in a state communicated with the end part of a threshing chamber, disposing a dust-sucking and discharging device in a state communicated with the end of the dust-discharging and treating chamber, and disposing a guide plate between the dust-sucking and discharging device and the rear half part of the dust-discharging and treating chamber, the guide plate being used for opening the dust-discharging and treating chamber in a grading chamber.