When an endoscope system is put into a special mode, first and second frame periods for performing imaging under first and second measurement light to measure an oxygen saturation level, a third frame period for performing imaging under normal light, and a fourth frame period for performing imaging under vessel detection light to detect blood vessels in specific depth are repeated. An oxygen saturation image, a normal image, and a vessel pattern image are produced and displayed in a tiled manner on a monitor in the form of moving images. When a freeze button is pressed during display of the moving images, the light intensity and exposure time to be used in the first to fourth frame periods of a still image recording process are calculated using an image that is captured immediately before pressing the freeze button. Still images are obtained with the calculated light intensity and exposure time.
