This paper newly proposes the active strobe imager (ASI) that can visualize the dynamic behaviors of internal organ to medical doctors within Human dynamic eye sight, so that they can get a hint for detecting the location of tumors in real time during operation. The ASI is composed of a nozzle for supplying a pulsated air jet to an internal organ, a strobe system for visualizing the dynamic behaviors, a camera for capturing the image at the moment of strobe flashing, and a monitor for displaying the dynamic motion of internal organ, respectively. Without the assistance of strobe, medical doctors can not see what is really happening in real time, since the frequency of air jet is even more than the range of human dynamic eye sight. After explaining the basic principle, we show a couple of experiments for both artificial and real human lungs. Through these experiments, we newly found that the ASI is really helpful for discovering tumors or other diseases hidden in internal organs. Movies are available in Website.