SUMMARYThis paper proposes a mechanism that supervises the learning data set for the classification from electromyogram to forearm motion. The supervising mechanism contains automatic data addition and automatic data elimination processes. It also contains manual data addition that is the same as our former algorithm. Both the automatic addition and elimination processes evaluate success or failure of classification from the continuity of the classifier's outputs. These processes assume that a person cannot change his motion within a certain interval. In experiments, a system with the supervising mechanism embedded classifies ten forearm motions from two channels of the electromyogram. First, this paper makes it clear that the proposed mechanism is effective by comparison with six settings, including the absence of a supervising pattern. Next, it is verified that the system can adapt to alteration of the operator's characteristics by a sensor-shifting test in which we move one sensor after the operator's training. From the experimental results, it is concluded that the proposed mechanism can adjust the generated decision boundaries for improvement of classification ability, and in addition is capable of tracking the alteration of the operator's characteristics through time.