To prevent the mixing of a polluted water, bacteria or fine dust in the ionized water or purified water discharged at the beginning by closing a valve means provided to a water injection pipe until the city water flowing in an electrolytic cell amounts to a specified amt. at the start of use.

The inflow of city water to a water feed pipe 12 at the start of use is detected by a pressure sensor 31, and a solenoid valve 60 is closed for a specified time by a control means 70 based on the detection. Accordingly, the outflow of the city water into an electrolytic cell 40 from a water injection pipe 16 is hindered, and the city water in the cell is entirely discharged to the outside through a water discharge pipe 15. As a result, the water bacteria, etc. remaining in the cell 40 are discharged to the outside, and the inside of the cell 40 is cleaned. When the amt. of city water necessary for the cleaning is supplied, namely, when the passage of the specified time is confirmed by a timer means 71, the solenoid valve 60 is opened by the control means 70, and the mixing of polluted water, bacteria or fine dust in the ionized water is prevented at the start of use.