PURPOSE: To easily adjust the classifying limit particle size of particles.

CONSTITUTION: The secondary air passing through the gaps between the respective louver plates of a louver 40 is sucked into a classifying chamber 20 and a free vortex is formed in the classifying chamber 20. The particles in the classifying chamber 20 are classified by the free vortex and a fine powder flows in a fine powder taking-out pipe 25 and a course powder flows in a discharge passage 30. An adjusting sleeve 45 is connected to the base stand part 42 provided with the respective louver plates 41 by screws and raised to cover the outer peripheral parts of the louver plates 41 to raise the inflow position of the secondary air flowing in the classifying chamber 20. By this constitution, a classifying limit particle size is reduced.