A self-propelled harvester thresher has a threshing and separating mechanism, a flat sieve device, and a sieve drum for the straw-chaff-grain mixture located between the threshing and separating mechanism and the flat sieve device, wherein the sieve drum is located above the flat sieve device and has a feeding opening and an outlet opening with a screw transporting the product from the feeding opening to the outlet opening, and the thresher is provided with a returning member located immediately before the outlet opening.
