PURPOSE: To obtain a controller for grading in a combine harvester capable of automati cally setting grading conditions with the amount of materials to be graded relatively to a travel speed without performing the initial setting.

CONSTITUTION: In a thresher obtained by equipping a grading air passage formed from a windmill with a grader for carrying out the winnowing and grading leaked down materials while transferring the materials which are to be graded and leaked down from a receiving net of a threshing chamber 2 to the rear, additionally installing a layer thickness detecting sensor for sensing the layer thickness of the materials to be graded and a grading performance regulating means in the leaked down material grading part of the grader, additionally providing a travel speed detecting sensor (G) in a travel device (A) or a transmission device interlocking therewith and constructing the grading performance regulating means so as to perform the stepwise automatic control based on the sensed value of the travel speed detecting sensor (G) and the layer thickness detecting sensor 32, the objective controller for grading in a combine harvester is constructed so as to change over the grading performance by the degree of change in the sensed value of the layer thickness detecting sensor 32 based on the sensed value of the travel speed detecting sensor (G) in the initial reaping.