An apparatus for measuring the concentration of carbon dioxide in water that can correct a reduction in measurement accuracy based on deterioration of a pH indicator is provided. A carbon dioxide concentration measurement apparatus includes a deterioration determining section that measures a change rate ΔA0 of an isosbestic point absorbance A0 and determines that the pH indicator solution is deteriorated when the change rate ΔA0 is reduced by a predetermined reduction rate or more. After the deterioration determining section determines deterioration of the pH indicator solution, a pH value computing section computes the pH value of the pH indicator solution using a corrected pH computation expression for correcting a deterioration of the pH value of the pH indicator solution on the basis of the change rate ΔA0 of the isosbestic point absorbance A0.