1. A method of controlling a robot having a manipulator formed by coupling a plurality of links at respective joint axes and having at least one redundant degree of freedom that is redundant with respect to task degrees of freedom, each of the joint axes being driven by a rotary actuator provided for each joint of the manipulator, comprising: calculating load torque of a respective rotary actuator on the joint axis of each link based on at least inertia force, centrifugal force or Coriolis force, and gravity force, each time a link position and orientation allowed by the redundant degree of freedom is changed, by a predetermined value, from an initial link position and orientation to a final link position and orientation, under a constraint of end-effector position and orientation set as target values; obtaining the link position and orientation at which the ratio of the load torque to rated torque of each of the rotary actuators is minimized, while the link position and orientation are being changed from the initial link position and orientation to the final link position and orientation; and providing a feed-forward value that gives rise to each load torque obtained when the ratio of the load torque to the rated torque of each of the rotary actuators is minimized, to a control command generated to the rotary actuator of each joint axis for achieving the end-effector position and orientation as target values.