An air classifier contains a cylindrical casing provided with at an upper part thereof a feed port to feed high pressure air and a powder material, an umbrella-shaped center core in the casing, and an umbrella-shaped separator core arranged downstream of the center core in the casing and including an opening at center thereof. The air classifier has a configuration containing a dispersion chamber to disperse the powder material, being surrounded by an inner wall of the upper part casing and the center core, and a classification chamber to classify the powder material into fine and coarse powders by centrifugation, being surrounded by the center core, separator core and inner wall of the casing. In the dispersion chamber provided are a louver ring containing guide slats circularly arranged at regular intervals, and a space encircling the louver ring and serving as flow passage of the air and powder material.