There is provided a method for treating for-treatment waste water containing an organic matter and a nitrogen compound, which can quickly and efficiently treat the for-treatment water containing the organic matter and the nitrogen compound and greatly reduce a power consumption amount, and which can be achieved by a relatively compact apparatus. A gist is that in treatment of the for-treatment water containing the organic matter and the nitrogen compound, the followings are carried out: an electrochemical treatment step of immersing at least a pair of electrodes at least partially in the for-treatment water to treat the nitrogen compound thereof by an electrochemical technique; and a biochemical treatment step of biochemically treating the nitrogen compound in the for-treatment water after completion of the electrochemical treatment step.