Regarding traffic accidents in Japan,there are many rear-end collisions. Most causes of rear-end collisions are by operators who are not concentrating. Operating a car without concentrating is very dangerous. Why do people not concentrate during operation why? Driver's fatigue is related to it. If a driver is in the state of fatigue,the body functions will fail. Reaction velocity, circumstantial judgment, and the degree of arousal mainly fail. If operating a car, it may become fatal. Therefore, we have to prevent operation fatigue. What should we do? A driver needs to take a break first. And researchers are developing a system which can detect fatigue. Therefore, we are studying it now. In the future, we will develop the system which warns of fatigue