PURPOSE: To provide an ionic water forming device for prolonging the life of a water purifier and preparing acid ionic water of high sterilization capability.

CONSTITUTION: A device comprises an electrolytic cell 1 electrolyzing service water to be supplied and forming alkali ionic water and acid ionic water and a water purifier 2 provided on the upstream side of the electrolytic cell 1 and purifying the service water, and a bypass 4 is formed between a water supply pipe 4 positioned on the upstream side of the water purifier 2 and the electrolytic cell 1, and a changeover means 6 is provided on a branching section 5 branching the water supply pipe 3 and the bypass 4. In the case alkali ionic water to drink is required, the service water is passed through the water purifier 2 by the changeover means 6 and fed to the electrolytic cell 1, while in the case acid ionic water for cleaning and sterilizing is required, the service water is passed through the bypass 4 without passing through the water purifier 2 by the changeover means 6 and fed directly to the electrolytic cell 1.