<;P>;PROBLEM TO BE SOLVED: To precisely measure CO<;SB>;2<;/SB>;dissolved in seawater. <;P>;SOLUTION: This instrument for measuring the concentration of CO<;SB>;2<;/SB>;in seawater is equipped with: an acidification part electrolyzing seawater to adjust the acidity of the seawater to pH 5 or below; and the CO<;SB>;2<;/SB>;detection part provided on the downstream side of the acidification part so as to detect CO<;SB>;2<;/SB>;contained in the seawater set to pH 5 or below in the acidification part by an infrared spectroscopic method. <;P>;COPYRIGHT: (C)2011,JPO&INPIT