Good hand know prevent as much as possible and the efficiency of the electrode makes it possible to perform the electrolytic solution such as sulfuric acid. Passed through the electrolyte in the electrolytic cell with an electrode of at least one pair of an anode and a cathode and, in the method delivered to deliver the electrolyte by supplying current to the electrodes, to the viscosity of the electrolyte in a range corresponding to the current density of the energization the electrolysis is carried out. Current density of 50A / or less than 10cP when the d㎡ the viscosity of the sulfuric acid solution as the electrolytic solution, the current density of 50A / d㎡ ~ less than 75A / d㎡ 8cP the viscosity of the sulfuric acid solution in the case of a current density of 75A / d㎡ excess ~ is the viscosity of the sulfuric acid solution to less than 6cP when the 100A / d㎡. In particular, while reducing electrode to know if the high-concentration sulfuric acid electrolytic solution with high current density by the diamond electrode may be hand delivered to process with high efficiency.