The authors propose a center of gravity control method for a manipulator/vehicle system to ensure that the system cannot fall down. Different from the manipulator avoiding tumbling is a very serious problem for the manipulator/vehicle system not fixed on the floor/ground tightly. Therefore, the authors consider an algorithm for controlling both the tip position of the end effector and the center of gravity of the manipulator and the payload being carried by the manipulator. This control algorithm was applied to the manipulator with the vehicle for man-robot cooperation. The trajectory of the manipulator is given by a human operator and the center of gravity is set so as not to tumble previously. An experiment was carried out to confirm the effectiveness of this control algorithm for the manipulator/vehicle system.