In this study, the load on waist during the lifting motion will be analyzed to know how much power have to be needed in actuator of the power assist suit. Also, a motion detection method which does not use myoelectric sensors will be proposed. The method which is using a myoelectric sensor might cause a malfunction due to noise. The proposed method is based on an encoder and a pressure sensor so that it is simple and less likely to cause a malfunction. In addition, the effectiveness of the proposed method will be confirmed through the experiment. The experiment were done for power asist suit of the motor type.