Abstract: An apparatus for classifying particles entrained by a solid-gas jet stream includes a feed nozzle, a cyclonic wall having an inner arcuate wall, and an auxiliary inner arcuate wall provided at an outlet port of the nozzle. The solid-gas stream is preliminarily bent along the auxiliary inner wall so that the particles are preliminarily or roughly classified into undersized and oversized particles by the action of the centrifugal force before they are classified by the cyclonic wall. The apparatus may include a collecting port disposed downstream of the nozzle outlet port and spaced slightly away from the inner arcuate wall of the cyclonic wall. The collecting port permits the apparatus to collect the undersized particles in a more effective manner.