PURPOSE: To keep ionized water producing function over a long period of time by preventing the precipitation of salts in a water electrolizing process and the adhesion of salts to the inside of an electrolytic cell to prevent the lowering of electrolytic power.

CONSTITUTION: Switches SW1, SW2 changing over the directions of a current to first and second electrode plates 11,12, the raw water inlet passage 15 connected to one end parts of electrolytic cells 10A, 10B in a branched state and the first and second alkali ion water passages 17a, 17b connected to the electrolytic cells 10A, 10B and meeting with a common alkali ion water collecting port 17 are provided. The first and second acidic ion water passages 18a, 18b connected to the other end parts of the electrolytic cells 10A, 10B and meeting with the common acidic ion water collecting port 18 on the downstream side of both cells and the changeover valves V1-V4 provided to ionized water passages 17a, 17b, 18a, 18b are contained.