The apparatus according to the present invention includes a level adjusting circuit that increases a gain of a G (or B) signal output from a color conversion circuit, a binarization circuit that forms a binarized image from this G signal and an edge detection circuit that extracts blood vessel position signals through edge detection based on this binarized signal. Then, the apparatus extracts RGB color signals making up a blood vessel image by using the above-described blood vessel position signals, increases the gains of these blood vessel color signals and then adds the blood vessel color signals to the color signals of an original image. This allows blood vessels to be displayed in high contrast to mucous membranes, etc. Furthermore, the apparatus can also amplify the R signal and B signal by using a signal obtained by differentiating the above-described G signal as a gain signal to highlight blood vessels.