In order to assist the perception-abilities of elderly parsons and/or handicapped parsons, the perception-assist have been studied. In the perception-assist, user's dangerous motion is modified to safety motion automatically by using several motion changing methods. On the other hand, it is revealed that human knee joint extension motion can be changed by vibrating hamstring muscles. The final goal of this study is to modify knee joint extension motion to desired motion by using vibration stimulation for lower-limb perception-assist. For this purpose, this study aims to find an effective method for knee joint motion change. In the experiment of this study, the tendons of lateral hamstring muscles and/or medial hamstring muscles are vibrated during knee joint extension motion. Furthermore, when vibration is added to both tendons of hamstring muscles, two patterns of the phase of vibration stimulation is added and the effect of vibration stimulation phase is estimated. The experimental results show that when vibration stimulation was added to both tendons of hamstring muscles, the effect of vibration stimulation to knee joint extension motion change is the largest.