An endoscope system comprising: a lighting means (11, 33) configured to apply illumination light to an object, broad band light in a visible range and narrow band light having a wavelength range in which oxyhemoglobin and deoxyhemoglobin have different absorption coefficients being used as said illumination light; an image information obtaining means (34, 70) configured to image said object under irradiation with said broad band light to obtain first image information, and to image said object under irradiation with said narrow band light to obtain second image information; a normal image producing means configured to produce a normal image having a wavelength component of said broad band light based on said first image information; an oxygen saturation level calculating means configured to calculate an oxygen saturation level of blood based on said second image information; a region determining means configured to determine in said normal image a hyperoxic region having said oxygen saturation level of a predetermined value or more and a hypoxic region having said oxygen saturation level of less than said predetermined value; a region processing means configured to apply a different type of process to each of said hyperoxic region and said hypoxic region, and to produce an oxygen saturation image; and a monitor device configured to display said normal image or said oxygen saturation image, characterized in that said region processing means is configured to apply both a white balance process as a color balance process, and a color enhancement process for enhancing a red component to said hyperoxic region, to apply a gain process to said hypoxic region to bring about color variations in said hypoxic region in accordance with difference in said oxygen saturation level in that said gain process varies color in said hypoxic region in accordance with a degree of said oxygen saturation level by adjustment of said pixel value of said hypoxic region, configured to apply an artificial color enhancement process for enhancing artificial colors to said hypoxic region, which is tinged with artificial colors different in accordance with a degree of said oxygen saturation level, and to not apply said white balance process to said hypoxic region, and to not apply said gain process to said hyperoxic region. a lighting means (11, 33) configured to apply illumination light to an object, broad band light in a visible range and narrow band light having a wavelength range in which oxyhemoglobin and deoxyhemoglobin have different absorption coefficients being used as said illumination light; an image information obtaining means (34, 70) configured to image said object under irradiation with said broad band light to obtain first image information, and to image said object under irradiation with said narrow band light to obtain second image information; a normal image producing means configured to produce a normal image having a wavelength component of said broad band light based on said first image information; an oxygen saturation level calculating means configured to calculate an oxygen saturation level of blood based on said second image information; a region determining means configured to determine in said normal image a hyperoxic region having said oxygen saturation level of a predetermined value or more and a hypoxic region having said oxygen saturation level of less than said predetermined value; a region processing means configured to apply a different type of process to each of said hyperoxic region and said hypoxic region, and to produce an oxygen saturation image; and a monitor device configured to display said normal image or said oxygen saturation image, characterized in that said region processing means is configured to apply both a white balance process as a color balance process, and a color enhancement process for enhancing a red component to said hyperoxic region, to apply a gain process to said hypoxic region to bring about color variations in said hypoxic region in accordance with difference in said oxygen saturation level in that said gain process varies color in said hypoxic region in accordance with a degree of said oxygen saturation level by adjustment of said pixel value of said hypoxic region, configured to apply an artificial color enhancement process for enhancing artificial colors to said hypoxic region, which is tinged with artificial colors different in accordance with a degree of said oxygen saturation level, and to not apply said white balance process to said hypoxic region, and to not apply said gain process to said hyperoxic region.