A subject irradiated with violet light and green light is imaged to obtain RGB signals, based on which a base image is produced. Frequency filtering processing is applied to the B signal to obtain a blood vessel extraction signal, in which a most superficial blood vessel, a superficial blood vessel, and a middle-layer blood vessel at different depths are extracted. Edge strength of each blood vessel in the blood vessel extraction signal is calculated. Display control processing based on the edge strength of each blood vessel is applied to the base image. Thereby, a first image or a second image is produced. In the first image, the most superficial blood vessel, the superficial blood vessel, and the middle-layer blood vessel are displayed in a distinguishable manner. In the second image, the most superficial blood vessel, the superficial blood vessel, and the middle-layer blood vessel are selectively enhanced or suppressed.