This paper presents a control method of multi-DOF power assistant robots for anatomical multi-axis joints such as the wrist and the ankle. It is difficult to calculate the accurate direction of human motion intention during manipulating an object due to discrepancy between the calculated force from F/T sensor and the real human intention. Only using an sEMG is not an adequate method of power assistance for unknown external perturbation in the anatomical multi-axis joint, because the sEMG signal cannot figure out where the intention vector exists during interactions. This paper proposes a robust control method of power-assistant robots for unknown external perturbation during manipulating an object by using both the F/T sensor and sEMG. The specific purpose of this study to control the exoskeleton robot for the wrist motion during manipulating an object, although the accurate intention vector of the wrist joint is unknown. It was verified that the proposed method generates the assisted power to follow the human motion intention even in the case of unknown external forces through experiments.