To easily regenerate an ion exchange membrane by providing a regenerating chemicals supply means supplying regenerating chemicals for regenerating the ion exchange membrane in an electrolytic cell to the electrolytic cell.

An electrolytic cell 1 has an anode chamber 3 equipped with an anode 2 and a cathode chamber 5 equipped with a cathode 4 and an ion exchange membrane 6 is provided between the anode chamber 3 and the cathode chamber 5. Chemicals in an acid tank 9 are sent by a pump 13 to be supplied to the anode chamber 3 by a raw water supply pipe 7a through an opening and closing valve 14 and chemicals in an alkali tank 10 are sent by a pump 15 to be supplied to the cathode chamber 5 by a raw water supply pipe 7b through an opening and closing valve 16 to perform electrolysis and, thereafter, alkali is supplied to one of the anode chamber 3 and the cathode chamber 5 from a regenerating chemicals tank 17 to regenerate the ion exchange membrane 6.