1. An apparatus comprising: means for casting visible light toward a reflective object at a frequency of no less than the critical fusion frequency; means for picking up an image of the object and outputting image data in accordance with the picked-up image; a light-intensity sensor monitoring the intensity of a light incident on said image pickup means and outputting a signal representing the level of the intensity of the incident light; an optical shutter of liquid crystal filtering the incident light; a light-intensity control circuit opening and shutting said optical shutter in accordance with the frequency of the casting of the visible light and controlling a duty cycle of said optical shutter in response to a level of said signal so as to control an effective transmissivity of said optical shutter; means for generating a picture signal in accordance with the image data; and means for displaying a picture of the object in response to the picture signal.