An electronic endoscope system having an endoscope, comprising: a light applying section adapted to apply at least three types of narrow band light having wavelengths within 400 nm to 600 nm as illumination light to an internal body part containing a blood vessel, two types of the illumination light out of the three types of the illumination light being narrow blue band light and narrow green band light, the three types of the illumination light include first narrow blue band light having wavelengths of 405 ± 10 nm, second narrow blue band light having wavelengths of 470 ± 10 nm, and third narrow green band light having wavelengths of 560 ± 10 nm; an image sensor (44, 90) adapted to capture an image of the internal body part irradiated with the illumination light; a blood vessel information obtaining section adapted to obtain blood vessel information based on a narrow band signal corresponding to the three types of the narrow band light and including a first narrow blue band signal, a second narrow blue band signal, and a third narrow green band signal, the blood vessel information including a depth of the blood vessel and a hemoglobin index; a brightness ratio calculating section adapted to calculate a first brightness ratio between the first narrow blue band signal and the second narrow blue band signal, and a second brightness ratio between the third narrow green band signal and the second narrow blue band signal; and a memory adapted to store in advance a correlation between the depth of the blood vessel and the hemoglobin index with respect to the first and second brightness ratios, wherein, the blood vessel information obtaining section is adapted to obtain based on the correlation stored in the memory the depth of the blood vessel and the hemoglobin index from the first and second brightness ratios a light applying section adapted to apply at least three types of narrow band light having wavelengths within 400 nm to 600 nm as illumination light to an internal body part containing a blood vessel, two types of the illumination light out of the three types of the illumination light being narrow blue band light and narrow green band light, the three types of the illumination light include first narrow blue band light having wavelengths of 405 ± 10 nm, second narrow blue band light having wavelengths of 470 ± 10 nm, and third narrow green band light having wavelengths of 560 ± 10 nm; an image sensor (44, 90) adapted to capture an image of the internal body part irradiated with the illumination light; a blood vessel information obtaining section adapted to obtain blood vessel information based on a narrow band signal corresponding to the three types of the narrow band light and including a first narrow blue band signal, a second narrow blue band signal, and a third narrow green band signal, the blood vessel information including a depth of the blood vessel and a hemoglobin index; a brightness ratio calculating section adapted to calculate a first brightness ratio between the first narrow blue band signal and the second narrow blue band signal, and a second brightness ratio between the third narrow green band signal and the second narrow blue band signal; and a memory adapted to store in advance a correlation between the depth of the blood vessel and the hemoglobin index with respect to the first and second brightness ratios, wherein, the blood vessel information obtaining section is adapted to obtain based on the correlation stored in the memory the depth of the blood vessel and the hemoglobin index from the first and second brightness ratios