When we look at a comfortable scene or feel relaxed, our brain waves generally exhibit /spl alpha/-wave signals in the frequency band of approximately 8 to 13 Hz. These /spl alpha/ waves particularly exhibit a 1/f fluctuation in which the corresponding power is inversely proportional to frequency 1/f /spl alpha/-wave signals obtained from test subjects listening to relaxing music was inputted to a robot manipulator. To evaluate the resulting motions, test subjects were asked to complete questionnaires while they watched two types of manipulator motions: a 1/f motion and a white-noise-like motion. The results indicated that 90% of the subjects felt comfortable while watching the 1/f manipulator motions.