In the progress of elderly society, the gait is important in order to live the independent life. Therefore, it is necessary to evaluate gait analysis simply. Our final goal is to propose the wearable gait analysis. In this paper, we have estimated floor reaction force vector using thin sensor. The floor reaction force vector during a walk is the direction of the body center of gravity. Moreover, the gap with the floor reaction force vector and the body center of gravity generates a rotation moment. We used this specific. Our evaluation method will be useful for developing sensors systems.