To provide a crystallizer capable of enhancing gas-liquid separation property and solid-liquid separation property withoutraising manufacturing cost and also without increasing installation space.
In the crystallizer 1, wastewater or wastewater and a part of treated water is fed to a reaction tank 2 from its lower part and air (gas) is fed, seed crystal being deposition cores is fluidized in an upward flow in the reaction tank 2, a chemical agent is added to treating object ions in the wastewater to deposit insoluble salt to the seed crystal to remove ions from the wastewater, and treated water after gas-liquid separation is discharged outside the reaction tank 2. Wherein, a tilted plate 9, by which an upper sectional area is narrowed once to be smaller than a lower sectional area, is installed at an upper part in the reaction tank 2, and a discharge port 15 for discharging remaining gas under the tilted plate 9 in the reaction tank 2 is formed on at least either one of the wall face of the reaction tank 2 or the tilted plate 9.