The concentration of impurities contained in ultrapure water or press water can be efficiently analyzed with high precision. A portion of a liquid to be measured is introduced into an absorption spectrometric portion 2c from a predetermined line. The liquid is irradiated with exciting light Le from an exciting light irradiation system 10, and a measurement objet region AS in which a photothermal effect of the impurities in the liquid is produced by the irradiation is irradiated with measuring light Lm from a measuring light irradiation system 20. A change in phase of the measuring light Lm is detected by a predetermined optical system and a photodetector 36, and the impurity concentration in the liquid is determined on the basis of the change in phase.