PURPOSE: To remove harmful heavy metal from waste water, containing the harmful heavy metal containing ferrous salt and alkali, in a short time at the normal temperature, by producing ferrite incorporaed with the harmful heavy metal by substituting ferrous salt ions with ferric salt ions by treating the waste water through anodic oxidation.

CONSTITUTION: A vessel ois filled with waste water which contains harmful heavy metal (e.g., Zn2+ and N2+) containing ferrous salt such as iron sulfide and alkali such a NaOh. Then, the waste water in the vessel is stirred uniformly without forming air bubbles in the liquid for anodic oxidation of ferrous salt ions, thereby producing ferric salt ions. Thus, a ferromagnetic precipitate composed of ferrite of large grain size having incorporated heavy metal ions in the liquid is produced in a short time. This precipitate is separaed to remove the harmful heavy metal from the waste water.