If a manipulator of a robot falls in local minima when expanding a node to generate a path, the manipulator may efficiently escape from local minima by any one of a random escaping method and a goal function changing method or a combination thereof to generate the path. When the solution of inverse kinematics is not obtained due to local minima or when the solution of inverse kinematics is not obtained due to an inaccurate goal function, an optimal motion path to avoid an obstacle may be efficiently searched for. The speed to obtain the solution may be increased and thus the time consumed to search for the optimal motion path may be shortened.