To remove flotation chippings and abrasive grains which are non-magnetic material, from grinding fluid.

The device of separating grinding sludge included in grinding liquid includes: a magnetic conveyer 6 attracting grinding sludge S with magnetic attraction force and moving that in a discharging direction; an accumulator 21 accumulating floating grinding sludge FS floating on a liquid surface of the grinding fluid L of the grinding sludge, in a predetermined accumulating area CA of a separating tank 4; a collector 22 immersed in the grinding fluid L so as to at least partially contact with the floating grinding sludge FS in regard to the floating sludge FS accumulated in the accumulating area CA by the accumulator 21, and then pulled up from the grinding fluid L to make the floating grinding sludge FS adhere to a surface; and a condenser 30 condensing the grinding sludge adhering to the collector 22 and pulled up from the grinding fluid L once. Massive grinding sludge KS condensed by the condenser 30 is put into the grinding fluid L again and settled down on a non-magnetic plate 5 to be discharged by the magnetic conveyer 6.