An endoscope system for observing a region of interest in a body cavity, the endoscope system characterized by comprising: a lighting section for applying illumination light, selected from two or more types of illumination light, to a region of interest; an imaging section for imaging the region of interest illuminated with the illumination light selected; an image processor for producing an observation image based on an image signal acquired from the imaging section, the observation image corresponding to the illumination light selected; a suspected-lesion detection section for detecting a suspected lesion in the observation image; an oxygen saturation calculation section for obtaining an oxygen saturation level of a blood vessel in the observation image; a judging section for judging whether the oxygen saturation level of the suspected lesion is in a hypoxic condition within a predetermined range; and a display section for displaying the observation image; characterized in that the lighting section selectively generates one of white light, mixed light in which the white light is mixed with blue narrowband light at a predetermined ratio, and two or more types of narrowband light each having an absorption coefficient varying with the oxygen saturation level, as the illumination light, and in that the image processor includes a special image processing section for combining a normal light image with a blue-enhanced image to produce a special image in which the blood vessel is enhanced, and the normal light image is produced based on the image signal outputted from the imaging section during illumination with the white light, and the blue-enhanced image is produced based on the image signal outputted from the imaging section during illumination with the mixed light. a lighting section for applying illumination light, selected from two or more types of illumination light, to a region of interest; an imaging section for imaging the region of interest illuminated with the illumination light selected; an image processor for producing an observation image based on an image signal acquired from the imaging section, the observation image corresponding to the illumination light selected; a suspected-lesion detection section for detecting a suspected lesion in the observation image; an oxygen saturation calculation section for obtaining an oxygen saturation level of a blood vessel in the observation image; a judging section for judging whether the oxygen saturation level of the suspected lesion is in a hypoxic condition within a predetermined range; and a display section for displaying the observation image; characterized in that the lighting section selectively generates one of white light, mixed light in which the white light is mixed with blue narrowband light at a predetermined ratio, and two or more types of narrowband light each having an absorption coefficient varying with the oxygen saturation level, as the illumination light, and in that the image processor includes a special image processing section for combining a normal light image with a blue-enhanced image to produce a special image in which the blood vessel is enhanced, and the normal light image is produced based on the image signal outputted from the imaging section during illumination with the white light, and the blue-enhanced image is produced based on the image signal outputted from the imaging section during illumination with the mixed light.