An ion elution unit generates metal ions by applying a voltage between electrodes. Terminals are formed integrally to the electrodes. An interval between the electrodes becomes narrower from an upstream side to a downstream side with respect to a water current flowing through an inside of a casing of the ion elution unit. Terminals that are so laid as to run from the electrodes out of a casing of the ion elution unit are disposed on an upstream side with respect to a water current flowing through an inside of the casing.