An electronic endoscope system includes a light source device for sequentially emitting light having different wavelength bands, an electronic endoscope for receiving reflected light of light sequentially illuminating a subject tissue containing a blood vessel in a body cavity and sequentially outputting an imaging signal corresponding to the wavelength band of the received light, an aligner for aligning images corresponding to imaging signals obtained using light having different wavelength bands outputted from the electronic endoscope, an image producer for producing an oxygen saturation level image representing the distribution of the oxygen saturation level in the blood vessel in a given depth from the imaging signals of the images aligned by the aligner, and an image display for displaying the oxygen saturation level image produced by the image producer.
