The purpose of the present invention is to obtain observed images in which the contrast of superficial blood vessels has been enhanced and to observe superficial blood vessels in more detail. A long cut filter (LCF)(48) is provided on the front surface of a blue semiconductor light source (35). Of the blue light (LB) emitted by the blue semiconductor light source (35), the LCF (48) cuts the long wavelength components at or above the wavelength (450 nm) of the intersection point (P) of the reflectances of the superficial blood vessels and the intermediate layer blood vessels in the reflection spectra of the superficial blood vessels present in the superficial layer of the mucosa of living tissue and the intermediate layer blood vessels present in the intermediate layer and generates a long cut blue light (LBlc1). A mixed light of said long cut blue light (LBlc1), green light (LG) and red light (LR) is irradiated on a region to be observed and an image is captured by an image pickup element (56). A highlighting section (70) performs processing on the image signal output from the image pickup element (56) to highlight the superficial blood vessels.
