An electronic endoscope has a video-scope with an image sensor, a light source that emits illuminating-light to illuminate an object, an image sensor driver, a luminance detector, one rotary shutter, and a brightness adjuster. The luminance detector detects a luminance of an object image on the basis of image-pixel signals read from the image sensor. The rotary shutter has a light-transmitting portion that transmits the illuminating light, and a shield portion that blocks the illuminating light. The brightness adjuster controls the rotary shutter to adjust an irradiation-interval of the illuminating-light in accordance with a charge accumulation interval. The brightness adjuster shifts a rotation-phase of the rotary shutter by changing a rotation-speed on the basis of the detected luminance, so as to maintain a brightness of the object image at a proper brightness.