A surface EMG signal is one of the most widely used signals as input signals to wearable robots. However, EMG signals that are used to estimate motions are not always available to all users. On the other hand, an EEG signal has drawn attention as input signals for those robots in recent years. The EEG signals can be measured even with amputees and paralyzed patients who are not able to generate some EMG signals. However, the measured EEG signal does not have one-to-one relationships with the corresponding brain part. Therefore, it is more difficult to find the required signals for the control of the robot in accordance with the intention of the user's motion using the EEG signals compared with that using the EMG signals. In this paper, both the EMG and EEG signals are used to estimate the user's motion intention. In the proposed method, the EMG signals are used as main input signals because the EMG signals have higher relative to the motion of a user in comparison with the EEG signals. The EEG signals are used as sub signals in order to cover the estimation of the intention of the user's motion when all required EMG signals cannot be measured. The effectiveness of the proposed method has been evaluated by performing experiments.