To provide a fluorine crystallization treatment method which enables the supply of phosphate ions and sulfate ions to a crystallization reaction tank.

The fluorine crystallization treatment method yields treated water of reduced fluorine by supplying fluorine-containing water to be treated, a crystallization agent, and the phosphate ions and the sulfate ions to the crystallization reaction tank and precipitating fluorine compounds onto seed crystals in the crystallization reaction tank to form pellets. This method can prevent the generation of white turbidity in the treated water, and enables stable and efficient crystallization and removal of fluorine even when the water to be treated contains high concentration of fluorine.