When an endoscope system (10) 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 (14) in the form of moving images. When a freeze button (16b) 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 (16b). Still images are obtained with the calculated light intensity and exposure time.
