An electronic endoscope system comprising: an illuminating device for projecting illumination light toward subject tissues inside a body cavity, including blood vessels, wherein said illumination light includes first, second and third narrowband rays (N1,N2) of different wavelength ranges from each other, at least one of the first, second and third narrowband rays having a central wavelength of not more than 450 nm and wherein the narrowband rays each have a wavelength range within limits of ±10 nm; an electronic endoscope having an imaging device for capturing and outputting image signals that represent luminance of said illumination light as being projected toward and then reflected from said subject tissues; a first narrowband signal obtaining device for obtaining first and second narrowband signals from said image signals, the first and second narrowband signals corresponding to the first and second narrowband rays respectively; a second narrowband signal obtaining device for obtaining a third narrowband signal from said imaging signals, the third narrowband signal corresponding to the third narrowband ray having a different wavelength range from the first and second narrowband rays, characterized in that the system further comprises a luminance ratio calculator for calculating a first luminance ratio (S1/S3) between the first and third narrowband signals and a second luminance ratio (S2/S3) between the second and third narrowband signals; a first storage device previously storing correlations between the first and second luminance ratios and the vessel depth and the oxygen saturation, and a vascular information acquiring device for acquiring vascular information about vessel depth and information about oxygen saturation representative of the percentage of oxygenated hemoglobin in the blood vessels from the first and second luminance ratios calculated by said luminance ratio calculator, with reference to said correlation stored in the first storage device. an illuminating device for projecting illumination light toward subject tissues inside a body cavity, including blood vessels, wherein said illumination light includes first, second and third narrowband rays (N1,N2) of different wavelength ranges from each other, at least one of the first, second and third narrowband rays having a central wavelength of not more than 450 nm and wherein the narrowband rays each have a wavelength range within limits of ±10 nm; an electronic endoscope having an imaging device for capturing and outputting image signals that represent luminance of said illumination light as being projected toward and then reflected from said subject tissues; a first narrowband signal obtaining device for obtaining first and second narrowband signals from said image signals, the first and second narrowband signals corresponding to the first and second narrowband rays respectively; a second narrowband signal obtaining device for obtaining a third narrowband signal from said imaging signals, the third narrowband signal corresponding to the third narrowband ray having a different wavelength range from the first and second narrowband rays, characterized in that the system further comprises a luminance ratio calculator for calculating a first luminance ratio (S1/S3) between the first and third narrowband signals and a second luminance ratio (S2/S3) between the second and third narrowband signals; a first storage device previously storing correlations between the first and second luminance ratios and the vessel depth and the oxygen saturation, and a vascular information acquiring device for acquiring vascular information about vessel depth and information about oxygen saturation representative of the percentage of oxygenated hemoglobin in the blood vessels from the first and second luminance ratios calculated by said luminance ratio calculator, with reference to said correlation stored in the first storage device.