Broadband light and narrowband light are simultaneously projected toward a subject. The subject is imaged by a color CCD to obtain a blue signal, a green signal, and a green signal. A base image is generated from the signals of three colors. Based on a luminance ratio B/G between the blue signal and the red signal, a B/G image is generated. A high frequency component is extracted from the B/G image to obtain a superficial-blood-vessel extracted image, and a medium frequency component is extracted from the B/G image to obtain a middle-deep-blood-vessel extracted image. Based on the base image and one of the superficial-blood-vessel extracted image and the middle-deep-blood-vessel extracted image, a blood vessel emphasized/de-emphasized image, in which the superficial blood vessels or the middle-deep blood vessels are emphasized or de-emphasized, is generated. The blood vessel emphasized/de-emphasized image is displayed on a monitor.
