PURPOSE: To avoid a resonance and attenuate a shaking caused by an external disturbance and a torque ripple quickly by a method wherein torques and a revolution on both ends of an elastic coupling means are estimated from the revolution of a motor and a motor current to compensate a current reference value.

CONSTITUTION: A system by which a motor is coupled with a load with an elastic coupling means is composed of a speed controller 1, a current controller 2, a torque conversion factor block 3, the transfer function block 4 of a rotation system, the transfer function block 5 of a mechanical shaft and the transfer function block 6 of a load. A monitor 10 is provided and the armature current ia of the motor and the motor speed nm are inputted to it. The monitor 10 estimates the output torque τs of the mechanical shaft, the load torque τl and nl as unknown parameters and outputs them. Those output signals are introduced into a compensation operating circuit 20 and the compensation operating circuit 20 generates a correction signal which corrects a current reference supplied from the speed controller 1 to the current controller 2 and outputs it.