To provide an electrochemical water treating unit which can suppress the adhesion of a hard component and can perform a stable operation by reducing the concentration ratio of the ions in the concentration chamber.

This electrochemical water treating unit is provided with an electrodialysis tank 1 obtained by bringing a plurality of units together so that electrode plates A, B2 and 3 are common, wherein each unit has a configuration in which a cation exchange membrane 4 and an anion exchange membrane 5 are alternately arranged, at least one deionization chamber and a concentration chamber are formed and the electrode plates A, B2 and 3 are disposed at both ends. In this configuration, a predetermined electric current can be supplied without applying high voltage and efficient deionization can be attained.