Broadband light (BB) and narrowband light (NB) are simultaneously projected toward a subject. The subject is imaged by a color CCD (44) to obtain a blue signal (B), a green signal (G), and a green signal (R). A base image is generated from the signals of three colors (B, G, R) . Based on a luminance ratio B/G between the blue signal (B) and the red signal (R), 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 (14).
