To suppress the occurrence of vibrations by controlling a drive means based on the difference between the estimated load acceleration and the PI- controlled load reference speed.

In a double inertia resonance system 110, two moments of inertia are connected to a shaft that has both flexibility and rigidity. A state observer 120 detects the torque (u) and position of a motor and estimates the speed (WL) and disturbance (TL) of the load. A load acceleration estimator 130 estimates the load acceleration based on the disturbance (TL) estimated via the observer 120 and the estimated twist torque (TT). A PI controller 140 performs the PI control based on the difference between the load reference speed (W*) and the estimated load speed (WL). The motor is controlled based on the difference between the estimated load reference speed (WL) and the PI-controlled load reference speed (W*). Thus, the system 110 can be stably controlled without causing vibrations.