Abstract: A combine for harvesting primarily spiked grains such as wheat, rye, barley, oats, and cereals such as buckwheat. The combine includes a rotating rotor arranged in a stationary casing along the direction of combine movement. An upper part of the casing is provided with helical guide fins mounted on the internal surface thereof. A lower part of the casing in a threshing zone is provided with a grate-type concave mounted under which is a conveyor to transport threshed product separated through the concave to a cleaning mechanism. The concave has openings of different open area and is made such that its portion having the openings of smaller size is located, with respect to the direction of combine movement, between a front edge of the concave and an imaginary extension of a helical line of the guide fins on the concave and enlarges in the direction of rotor rotation.