PURPOSE: To unnecessitate using chemicals such as an acid or concentrated salt water for the regeneration of a softening means by supplying a water softened by a cation exchange resin to an electrolytic cell and supplying an acidic water produced in the electrolytic cell to the cation exchange resin to regenerate.

CONSTITUTION: A water to be electrolyzed is detected by a feed water detecting sensor 1, purified in a purifying part 2, softened in a softening part 4 through a rotary valve 3 and supplied to the electrolytic cell 8 through a rotary valve 5, a three way solenoid valve 6 and a check valve 7. The electrolytic cell 8 is divided into an anode 10 side and a cathode 11 side by a semipermeable diaphragm 9 and an electrolyzing voltage is impressed to the electrodes from an electrolyzing electric source 12. Then, the electrolyzed ionic water is continuously produced, an alkaline water in the cathode side is discharged from an intake passage 15 and an acidic water in the anode side is discharged from a discharge passage 14. At the time of regenerating the ion exchange resin, the acidic water is reversed to the softening part 4 and ions of the ion exchange resin are replaced by hydrogen ion by switching the rotary valves 3, 5 and the three way solenoid valve 6 by a control part 16.