Previous researches reported that a lane change is the main cause of vehicle accidents. Therefore, inferring behaviors in other drivers and alarming to a driver are crucial tasks for safety. In this paper we propose a method to estimate lane change intentions in other drivers using Hidden Markov Models (HMMs). Comparing the proposed method with previous researches, we confirmed this method has higher accuracy to detect a lane change in other vehicles. And the method can recognize a slow lane change which is remained as a problem.