To significantly reduce the expense for disposal of sludge as an industrial waste when the sludge is disposed of.

A cyclone classifier 1 includes a linear pipe 2 having a suction port 4 and a funnel tube 3. If sludge S mixed with chips K and abrasive particles T is sucked from the suction port 4, the chips K and the abrasive particles T swirl inside the linear pipe 2. Since the chips K has a large specific gravity, the chips K fall downward, and is made to flow toward a discharge pipe 7 at the lower end while swirling in the funnel tube 3, and further are recovered in a chips recovery case from the discharge pipe 7. Further, the abrasive particles T are sucked by a suction device and recovered in the abrasive particle recovery case from a suction extension pipe 9 through a suction pipe 8. The chips K are recycled and used, and the abrasive particles T are treated as the industrial waste.