PROBLEM TO BE SOLVED: To provide a light measurement system capable of improving correctness of estimation of absorbance component density.SOLUTION: In an electronic endoscope system 15 shown as one example of the light measurement system, an observed portion is irradiated with an excitation light to excite Indocyanine green injected in a blood vessel to allow it to emit a light, and the Indocyanine green is subjected to image pickup to estimate the depth of the blood vessel from the surface of the observed portion on the basis of an image pickup signal obtained by the image pickup. Further, the oxygen saturation of hemoglobin is estimated on the basis of an image pickup signal obtained by irradiating the observed portion with at least two kinds of narrow band lights having different wavelength band. In estimating the oxygen saturation, any one or both of the following is (are) executed: selecting a wavelength set of the narrow band light or changing an estimation algorithm of the oxygen saturation so that the observation conditions meet a result of estimation of the depth of the blood vessel.
