In a mobile robot, the actuator characteristics are dynamically or statically controlled, during motions of an entire robot body in the course of falldown or descent, to realize stable highly efficient motions. In each stage of the falldown motions, the characteristics of each joint site taking part in controlling the stable area are set so that the low range gain is low, the quantity of phase lead is large and the viscous resistance of the motor is large, in such a manner that these joint sites may be positioned to high accuracy in a controller manner to increase orientation stability. This assures the positioning accuracy of the joints as main component for controlling the quantity .DELTA.S/.DELTA.t as a reference in controlling the falldown motions of the robot body to increase the motion stability.