The present invention relates to techniques for separating granular materials according to their size, and may be used in agriculture for sifting wheat or products derived therefrom, in the cereal milling and feed-mill industry as well as in the coal, ore extraction and construction material industries. This separator for granular materials comprises a row of concave sifting surfaces (1) arranged in a zigzag configuration under one another, wherein said surfaces are in the shape of cantilevered fingers (13) separated by a gap. The sifting surfaces (1) include sections with a concavity angle α and a length l that depend on the pitch of their height disposition h according to the relation 0.5 < αh/l < 1.4. The separator further includes an additional row of sifting surfaces (2) where the gap between the fingers (13) is smaller than that in the main row. The upper sifting surface (2) of the additional row is mounted above at least one third of the sifting surfaces (1) in the main row, but below the end of at least the first sifting surface of said row from the top.