An electronic endoscope system includes a light source device for sequentially emitting plural kinds of light having different wavelength bands, an electronic endoscope for outputting image data of acquired images corresponding to the plural kinds of light sequentially illuminated to a subject tissue containing blood vessels, a setter for setting a blood vessel characteristics amount from the image data, a setter for setting a region of interest in the acquired image based on the amount, an image producer for producing a first oxygen saturation level image representing a distribution of an oxygen saturation level in the blood vessel from the image data, and an image display for displaying in simulated color a second oxygen saturation level image in which the oxygen saturation level within the region of interest is selectively enhanced.
