To effectively remove fluorine.

Waste water containing fluorine, ammonia, acetic acid, and phosphorous is treated biologically in a nitrification tank 5, a denitrification tank 6, an oxidizing tank 7, and a sedimentation tank 8 to remove ammonia and acetic acid. Fluorine is solidified to calcium fluoride in a calcium reaction tank 1. Flock is coarsened and phosphorous is removed at the same time in an inorganic coagulant reaction tank 2 and a polymer coagulant reaction tank 3. Clarified treated water is obtained in a settling tank 4.