To provide a cutting fluid filtering device which is stably usable over a long period to always effectively remove magnetic and non-magnetic material sludge from a cutting fluid while effectively preventing undesired discharge of the cutting fluid to be capable of re-circulating the sufficiently cleaned cutting fluid in a machine tool.

A cutting fluid discharged from a machine tool is supplied to a magnet separator tank 1, after separating chips or the like of magnetic material, to be supplied to a dirty tank 2 having a sloped bottom surface and stirred, and the cutting fluid, after it is sucked by a first pump 11 from in the vicinity of the lowermost part of this sloped bottom surface and filtered by a filter 3, is supplied to a clean tank 4 and re-circulated in the machine tool by a second pump 14.