1. An actuator control device for force-controlling a joint driving actuator according to a commanded joint force command value τ a , the actuator control device comprising: means for detecting a joint value q at an output stage of the actuator; means for detecting an action force τ e in a joint driving direction at the output stage of the actuator; means for determining an instructed driving force τ to the actuator, on the basis of an ideal response model of the actuator which specifies the relationship of a joint value acceleration target value achieved as the actuator responds ideally when a joint force command value τ a , the action force τ e , and a joint value velocity obtained by time-differentiating the joint value q are given; wherein the means for determining an instructed driving force applies a disturbance observer to determine the driving force τ of the actuator; wherein the disturbance observer estimates a driving force which has acted on the joint on the basis of the joint value velocity obtained by time-differentiating the joint value q detected by the means for detecting a joint value q when the joint actuator is driven by the driving force τ determined by the means for determining an instructed driving force, and subtracts the estimated driving force from the driving force τ to calculate a disturbance joint force τ d ; and a low pass filter is used to prevent the divergence of the system.