An electronic endoscope system includes a light source device, an electronic endoscope for sequentially illuminating a subject tissue containing a blood vessel inside a body cavity with the light, and sequentially outputting image data of wavelength bands of the subject tissue corresponding to the different wavelength bands of received reflected light, a calculator for calculating a blood vessel characteristics amount in a subject tissue from the image data, a calculator for calculating an oxygen saturation level in the blood vessel from the image data, an image producer for producing a reference image of the subject tissue from the image data, an extractor for extracting a region of interest from the reference image, a producer for producing an enhanced image, and a display for displaying the enhanced image.
