The problem of the present invention is to provide a method or the like for producing reduced water (hydrogen-enriched water), which is effective for various diseases caused by active oxygen, more efficiently than the conventional methods, by putting metallic magnesium or the like in water. Adding a metal such as magnesium, together with a solid phase contained in an anode of an oxidation-reduction reaction, to water increases the saturating amount of magnesium ions, and improves deterioration due to magnesium hydroxide being precipitated on the surface of the metallic magnesium. Thus, the abovementioned problem is solved.
