NOVELTY - A water purifier consists of an ion-exchange membrane (34,35,34') arranged between an anode (32) and a cathode (31), a cathode chamber (41) filled with a conductive material (36), a cathode-side concentration chamber (42), a desalination chamber (43), an anode-side concentration chamber (44), and an anode chamber (45). The ion-exchange membrane which divides the cathode chamber and the cathode-chamber side concentration chamber is a bipolar film (33) or a monovalent cation permselective cation exchange membrane.    USE - Water purifier is used for manufacturing pure water from city water, well water, or industrial water, for use in fuel-cell power generating devices (all claimed).    ADVANTAGE - The water purifier prevents adhesion of scale to cathode or ion-exchange resin, by preventing movement of calcium or magnesium ion from cathode-side concentration chamber to cathode chamber. The water purifier is compact and eco-friendly. Salt-water replenishment and acid-alkali regenerated wastewater treatment are eliminated.    DETAILED DESCRIPTION - A water purifier consists of an ion-exchange membrane (33,34,35,34') arranged between an anode (32) and a cathode (31), a cathode chamber (41) filled with a conductive material (36), a cathode-side concentration chamber (42), a desalination chamber (43), an anode-side concentration chamber (44), and an anode chamber (45). An electric deionization apparatus is formed by filling the cathode-side concentration chamber, desalination chamber, and anode-side concentration chamber with an ion exchanger. The ion-exchange membrane which divides the cathode chamber and the cathode-chamber side concentration chamber is a bipolar film (33) or a monovalent cation permselective cation exchange membrane. To-be-processed water is flown into the desalination chamber in a state in which electricity supply is stopped or electricity supply is controlled to a current density of 1000 mA/dm2 or less. An executing unit of ion-exchange type pure-water manufacture operation mode is provided for carrying out ion exchange by the ion exchanger (37) of desalination chamber. Pure water is flown out of the desalination chamber.    DESCRIPTION OF DRAWING(S) - The drawing shows a systematic diagram of the ion-exchange system.    Cathode (31)    Anode (32)    Bipolar film (33)    Ion-exchange membranes (34,34',35)    Conductive material (36)    Ion exchanger (37)    Cathode chamber (41)    Cathode-chamber side concentration chamber (42)    Desalination chamber (43)    Anode-chamber side concentration chamber (44)    Anode chamber (45)