PROBLEM TO BE SOLVED: To provide an endoscope system capable of acquiring biological numeric information of high objectivity without depending upon an illumination condition nor a photographing condition, and the operation method thereof.SOLUTION: A specific mode of one between a normal mode for measurement and a special mode for measurement is set. The light emission amount of illumination light corresponding to the specific mode is selected with reference to a light emission amount storage part 24. A light source control part 21 fixes to the selected light emission amount of the illumination light, and controls the illumination light so as to be emitted. A brightness information calculation part 65 calculates the present brightness information of an observation object, and displays the present brightness information on a monitor 18. An image control part 70 performs at least one between display control of the monitor 18 and control of a still picture acquisition instruction on the basis of the brightness information.SELECTED DRAWING: Figure 2
