To extract a vibration excited by abnormal conditions in the rotation system of a motor or the like, without using any dedicated instrument for measuring the excited vibration when the abnormal conditions arise.

A disturbance component calculation unit 3 calculates a torque disturbance τd included in a motor current command si on the basis of the motor current instruction si and a motor velocity vm. A rotation-synchronous disturbance component extraction unit 4 extracts a magnitude of the torque disturbance τd whose period is synchronized with a rotation frequency of the motor 2 on the basis of the torque disturbance τd calculated by the disturbance component calculation unit 3. A rotation-frequency synchronous vibration increase decision unit 8 determines an increase of a rotation-frequency synchronous vibration when an output value from the rotation-synchronous disturbance component extraction unit 4 becomes equal to or more than a threshold.