To improve electrolysis efficiency by arranging two electrolytic cells communicated with each other in series.

An anodic water generated by the electrolysis in a 1st electrolytic cell 20 and discharged from an anodic chamber 22 is fed to the lower part of an anodic chamber 23 of a 2nd electrolytic cell 21 and a cathodic water generated by the electrolysis in the electrolytic cell 20 and discharged from a cathodic chamber 24 is fed to the lower part of a cathodic chamber 25 of the electrolytic cell 21 and is discharged from pipe opening parts 26, 27 of the upper part of the cathodic chamber of the electrolytic cell 21. A cathode 28 and an anode 29 are connected to each other in series and DC voltage is impressed between an anode 30 and a cathode 31. As a result of the constitution, the electrolysis efficiency is improved since current flowing to both electrolytic cells is decreased, the heat generation in the current circuit of the electrolytic cell is reduced and further, the gasification is decreased to reduce the generation of bubbles.