A gait generator determines a desired motional trajectory and a desired object reaction force trajectory of an object 120 for a predetermined period after the current time by using an object dynamic model while supplying, to the object dynamic model, a model manipulated variable (estimated disturbance force) for bringing a behavior of the object 120 on the object dynamic model close to an actual behavior, and provisionally generates a gait of a robot 1 for a predetermined period by using the aforesaid determined trajectories. Based on the gait and an object desired motion trajectory, a geometric restrictive condition, such as interference between the robot 1 and the object 120, is checked, and a moving plan for the object 120 or a gait parameter (predicted landing position/posture or the like) of the robot 1 is corrected as appropriate according to a result of the check, so as to generate a gait of the robot 1. Thus, a desired gait that satisfies a predetermined geometric restrictive condition related to the interference between the robot 1 and an object is generated by reflecting an actual environmental condition in real time while carrying out the operational control of the robot 1.