A dynamics simulation device for dynamically simulating physical interactions acting on a plurality of objects under an environment where the objects coexist is disclosed. The device includes: nominal value providing means for providing a nominal value Λn of an operational space inertial matrix; nominal inertial force calculating means for calculating a nominal inertial force acting on the operational space by the use of the nominal value Λn of the operational space inertial matrix and a target acceleration value of the physical quantity x; a disturbance observer estimating forces other than the nominal inertial force acting on the operational space as a disturbance; and means for calculating the force f acting on the physical quantity on the basis of the nominal inertial force and the estimated disturbance fd.