The present paper concerns a man-machine interface system for realizing the communication of a rather difficult information, which is unable to represent by the numerical method, such as an emotion of the artist. Since the emotion is expressed by action rather than word, the pattern of the tact movement for conducting synthesizer has been controlled by constructing the detecting and processing systems in real time. The tact, which is the most important input device has been made with high sensitivity of variation of speed without any effect from the swing directions, range and speed. The processing system has the sensitivity for detecting the degree of skillfulness, and then by using this parameter, the present system can conduct the synthesizer in the best condition corresponding to individual operators.