Information for assisting a doctor based on the oxygen saturation of an observation target is presented. An endoscope system includes a light source device, an image sensor, an oxygen saturation calculation unit, a distribution pattern generation unit, a disease state score calculation unit, and a monitor. The light source device emits light to irradiate the observation target. The image sensor images the observation target with reflected light of the light, and outputs an image signal. The oxygen saturation calculation unit calculates an oxygen saturation of the observation target based on the image signal. The distribution pattern generation unit generates a distribution pattern showing the distribution of the oxygen saturation. The disease state score calculation unit calculates a disease state score indicating the disease state of the observation target based on the distribution pattern. The monitor displays the disease state score or information based on the disease state score.
