PROBLEM TO BE SOLVED: To display an image with a blood stream pattern highlighted, and display information that realizes intuitive understanding of whether or not a site having the blood stream pattern is a site of lesion.SOLUTION: An endoscope system emits oxygen saturation measuring light and blood vessel highlighting illumination light to a specimen alternately. By using a color imaging element to image the specimen, the system obtains image data for two frames. Out of the image data for two frames, the system allocates blue image data Bs, which is obtained at the time of emission of the oxygen saturation measuring light, to a B channel of a display device 14, and allocates blue image data Bn and green image data Gn, which are obtained at the time of emission of the blood vessel highlighting illumination light, to a G channel and an R channel of the display device 14, respectively. Accordingly, the display device 14 displays a second narrow-band image with a color of a surface blood vessel changed only at the time of low oxygen saturation while highlighting the surface blood vessel and a medium-deep blood vessel.
