First to fourth narrow band light N1 to N4 is sequentially applied to an observation object by rotating a rotary filter for special observation set in an optical path of a broad band light source. A blood vessel enhanced image in which a superficial blood vessel and a middle to deep-layer blood vessel are enhanced is produced based on reflection images of the first and fourth narrow band light N1 and N4. An oxygen saturation image, which images an oxygen saturation level of hemoglobin in blood, is produced based on reflection images of the second to fourth narrow band light N2 to N4. The produced blood vessel enhanced image and the oxygen saturation image are displayed side by side on a monitor.
