To provide a method for operating an electrically ionizing apparatus that is capable of keeping the water quality of produced water good when the operation of the electrically ionizing apparatus is restarted.

In the method for operating the electrically deionizing apparatus which has an anion exchange membrane 13 and a cation exchange membrane 14 arranged between an anode 11 and a cathode 12 to form a condensation chamber 15 and a desalting chamber 16 and which has an ion exchanger 10 charged in the deslating chamber 16, a voltage is applied between the anode 11 and the cathode 12 to suppress the transfer of ions from the condensation chamber 15 to the desalting chamber 16 when production of deionized water by use of the apparatus is being stopped by interrupting supply of raw water.