A magnetic separator for purifying coolant including sludge mainly comprising needle-shaped chips for the purpose of recycling. A comb-type guide plate formed of a magnetic substance material is provided before a squeezing roller, in such a manner that convex and concave portions are in conformity with the magnetic lines of force produced by the arrangement of magnets of a fixed magnet-group cylinder stored in a rotary cylinder. Thus, magnetic flux curtains are formed between the convex portions and the rotary cylinder. Needle-shaped chips which have come as attracted sludge standing in the shape of a jet on the outer peripheral surface of the rotary cylinder are interrupted from going ahead by the magnetic flux curtains, and become accumulated sludge, and are led to lying attracted sludge on the left and right sides. Thus, the attracted sludge is prevented from stabbing a squeezing roller, and operations of extracting liquid from the sludge are continued without causing any trouble.