In order to assist not only motor function but also perception ability to perceive surrounding environment, a power-assist robot which has perception-assist function has been developed. By using additional external force with some actuators, the robot automatically modifies user's motion in perception-assist when the robot detects a possibility of accidents such as collision between user and obstacles. On the other hand, possibility of another perception-assist method which does not use additional external force for modifying user's motion has been studied recently. Kinesthetic illusion generated by adding vibration stimulation has a possibility for motion modification. During elbow flexion/extension motion, Triceps brachii plays an important role. Therefore, it is necessary to investigate the possibility of motion change by adding vibration stimulation on triceps brachii for perception-assist on upper limb. In this study, vibration stimulation is added to triceps brachii during one continuous flexion motion of elbow angle. From the results of experiments, some interesting features of motion change generated by vibration stimulation to triceps brachii is obtained.