A highly reliable image in which an oxygen saturation level of hemoglobin in blood is accurately visualized is displayed. A color image sensor (60) captures a reflected image of narrowband light having a wavelength range in which an extinction coefficient varies with a change in an oxygen saturation level of hemoglobin in blood. Thereby a blue signal (B1), a green signal (G1) , and a red signal (R1) are obtained. The color image sensor captures a reflected image of white light. Thereby a blue signal (B2), a green signal (G2), and a red signal (R2) are obtained. Only an oxygen saturation level, out of two or more types of biological functional information including a blood volume and the oxygen saturation level, is obtained based on the blue signal (B1), the green signal (G2), and the red signal (R2). The oxygen saturation level is visualized to produce an oxygen saturation image.
