To effectively suppress resonance, through a simple improvement, even when the resonance takes place at a frequency near a sampling cycle for torque command calculation, in a motor servo system.

An angular acceleration α for a motor is detected with a specified sampling cycle, and a resonance-suppression correcting value (d) is calculated according to the angular acceleration α for each sampling cycle, and the resonance suppression correcting value (d) is added to a torque command value τ* of speed control loop for each sampling cycle. The resonance- suppression correcting value (d) of each sampling cycle for a specified numbers is stored, and a resonance-suppression correcting value d(N-n) which is calculated with a sampling cycle (N-n) corresponding to a specified delay cycle number (n) is added to the torque command value τ* at a current sampling cycle N.