<p>A system for separating crystals from a sludge or water separated from a sludge through a concentration or dehydration treatment. It is satisfactory in both of phosphorus removal and recovery, and MAP having a satisfactory purity is recovered. It enables a stable treatment to be conducted with a high MAP recovery without clogging the liquid cyclone. An embodiment of the invention is a crystal separator which is an apparatus for separating crystals from a sludge or water separated from a sludge through a concentration or dehydration treatment. It is characterized by having: a liquid cyclone into which the sludge or separated water is introduced and in which the crystals contained therein are separated; and a return pipe (A) through which the sludge or separated water which has flowed out through an overflow riser of the liquid cyclone is returned to a sludge or separated-water introduction part of the liquid cyclone.</p>
