A new training system for standing up using lift mechanism is proposed considering safety of patients and effectiveness of training. From the view point of the effectiveness of training, patients have to use full standing up ability. Trajectory of the standing up process to decrease knee joint moment is considered. Joint moment in standing up process is estimated by using wearable motion sensors and simple force plate and optimum lifting force is calculated from the estimated joint moment to minimize the support force. Experiment is carried out and results show the effectiveness of the proposed training system.