The invention provides an endoscope system for generating an oxygen saturation image that can be used for various medical applications, such as oxygen saturation monitoring during surgery. A clip 141 is attached to the surrounding tissue of a tumor CN from the luminal side. The tissue to which the clip 141 is attached becomes an ischemic part CL. An oxygen saturation image is generated from image information obtained by imaging the tissue on the abdominal cavity side. In the oxygen saturation image, the ischemic part CL is displayed as a low oxygen region. Accordingly, it becomes easy to find the location of the tumor CN even from the abdominal cavity side.
