Provided is an endoscope system capable of emphasizing a slight difference in color tone. An observation target in a body illuminated by red, green and blue light R, G and B at a first light emission ratio is imaged by an image pick-up sensor 48, and an image signal of a first color, an image signal of a second color, and an image signal of a third color are output. The light emission ratio of the red, green and blue light R, G and B is changed from the first light emission ratio to a second light emission ratio, and the amount of the red, green and blue light R, G and B is controlled so that the image signal of the second color or the image signal of the third color matches the signal level of the image signal of the first color.
