A method and device for regenerating an ion exchanger can regenerate an ion exchanger easily and quickly, and can minimize a load upon cleaning of the regenerated ion exchanger and disposal of waste liquid. A method for regenerating a contaminated ion exchanger includes: providing a pair of a regeneration electrode and a counter electrode, a partition disposed between the electrodes, and an ion exchanger to be regenerated disposed between the counter electrode and the partition; and applying a voltage between the regeneration electrode and the counter electrode while supplying a liquid between the partition and the regeneration electrode and also supplying a liquid between the partition and the counter electrode.