Rescue robots are expected to perform works in hazardous areas. However, when the robot runs on a rough terrain, fatal rollover falling sometimes occurs. Therefore, we propose a tumble-risk-assessment system, which calculates a normalized energy stability margin by using a 3D depth sensor. Moreover, a control system to avoid the tumble situation by moving the sub-crawlers automatically is proposed. We implemented the proposed systems to a real robot, carried out experiments, and confirmed the effectiveness of the proposed method.