PURPOSE: To recover efficiently a grinding fluid for reuse, by filtering the grinding fluid contg. chips produced from a grinding attachment by using a magnetic separator, a liquid cyclone and a filter in combination.

CONSTITUTION: A grinding fluid 6 contg. chips produced from a grinding attachment 1, is introduced into a magnetic separator 2 where the chips 7 are roughly separated. Then the grinding fluid 8 from which chips 7 are roughly separated, is introduced into a liquid cyclone 11 to divide it into the grinding fluid 13 contg. fine chips and the grinding fluid 14 contg. coarse chips. The latter is introduced into the magnetic separator 2. The former is introduced into a filter 15 for filtration. Filter cake 20 is introduced into a sludge bag 17. Filtrate 19 is introduced into a clean tank 16, and recycled to the grinding attachment 1 by a pump P3 for reuse. In this way, the load of the filter 15 is reduced and the process enables stable filtration accuracy to be obtd.