PURPOSE: To provide a method and device for automatically adjusting a plant.

CONSTITUTION: In this method, a plurality of sine wave signals to a plant 16, frequency responses of the plant to the sine waves are measured to detect a resonance frequency of the plant. then a coefficient of at least one filter is calculated so that the resonance is suppressed when the filter is applied to the plant. Then at least one sine wave whose frequency is actually equal to a cross over frequency of the system is applied to at least one filter 50 and the plant, the frequency response is measured and the response of the amplitude and phase of the filter and the plant at the frequency is calculated. Then a coefficient of a compensation device 52 is calculated so that the combination of the device 52 with the filter 50 and the plant 16 produces a predetermined system response. The device to execute the above method is disclosed.