FIELD: mechanical engineering. SUBSTANCE: proposed invention relates to the field of separation of bulk materials in gas flows and can be used in construction, chemical, mining, metallurgical and other industries for fractionation of bulk materials by size. The air classifier of bulk materials includes a classification shaft, a feed pipe of the initial bulk material, a distributor of the initial bulk material and pipes for the output of large and small fractions. The classifier is equipped with a system of rigidly fixed coaxial, upward-facing, truncated pyramids that form slit gaps along the perimeter. The perimeter of each lower pyramid is smaller than the upper one. The distributor of the source material is made in the form of a hollow pyramid facing upwards with the base, rigidly and coaxially fixed over a system of coaxial truncated pyramids. EFFECT: increased efficiency of fractionation of bulk materials, as well as increased quality of particle size separation. 1 cl, 2 dwg.