Abstract: Provided are novel technical means for obtaining useful knowledge in practical application of antioxidation action of dissolved hydrogen and in practical application of active oxygen scavenging action in water. Based on the temporal profile of the difference between the dissolved oxygen amount measured with forcibly dissolving hydrogen and the dissolved oxygen amount measured with blowing any other gas than hydrogen, the reaction between dissolved hydrogen and dissolved oxygen is quantitatively evaluated. Based on the temporal profile of the difference between the dissolved oxygen amount measured with making a photosensitizing dye contained in water and with forcibly dissolving hydrogen therein, and the dissolved oxygen amount measured without making a photosensitizing dye contained in water and with forcibly dissolving hydrogen therein, the reaction between dissolved hydrogen and dissolved oxygen is quantitatively evaluated.