A blood vessel pattern or an irregular pattern is made clear while maintaining the brightness. A blue signal B, a green signal G, and a red signal R are obtained by imaging a subject illuminated with white light W using a color CCD 44. Based on these signals B, G, and R, a normal light image in which a wavelength component of a visible light region is included is generated. Based on the signals B, G, and R, a brightness signal I ((B + G + R)/3) showing the average brightness of the subject is generated. A pixel region exceeding the fixed threshold value Th1 of the brightness signal I is extracted as a superficial microstructure P, such as a pit pattern. A microstructure enhancement image 72 is generated by combining the normal light image with a superficial microstructure image 70 obtained by extracting the superficial microstructure P. The generated microstructure and blood vessel enhancement image 72 is displayed on a monitor 14.
