Abstract: In a cyclone classifier wherein the material to be processed is swirled in a tubular casing having a conical lower portion and classified, a cylindrical body is provided in the casing, so as to surround the lower end of a fluid outlet pipe and extends downwardly below an inlet port for the material to be processed, so that the sectional area of passage for the material to be processed swirled in the casing will be made smaller, thus increasing the classifying point while keeping the pressure loss at a minimum. From another aspect, annular pipes formed with fluid inlet ports are provided around the outer periphery of a lower part of the casing so as to communicate with the casing so that gases or liquids will be blown into the lower part of the casing through these pipes to form a swirling current, thus allowing the material to be processed to be reclassified thereby increasing the classifying point.