The aim of this study is to design a electrogoniometer for the measurement of three dimensional human elbow joint rotations. Using this device and visual monitor, we measured the angle of elbow joint rotations during the goal-directed movements. And we extracted myoelectric signals(MES) to verify the inter-relationship of elbow joint activities and constructed a system for the analysis of the spectrum for MES. The data obtained from this system will be used for the controller signal of prosthetic arm.