To provide a control system for realizing a oscillation reducer capable of applying a small fin and reducing driving power.

A first computation result as data for setting continuous time series signals for a period of time or longer corresponding to a oscillation cycle to be reduced in a ship equipped with a control device and a second computation result as data for instantaneously setting response signals in accordance with input signals from a sensor are combined for setting output signals for controlling an actuator. Values for parameters required for computation are calculated in accordance with the time series data input from the sensor for measuring the movement of a hull and the frequency analysis results of the time series data for the estimated movement of the hull accompanying the drive of the set actuator. The computed parameters are cyclically changed within the twice of a continuous period of time for the time series data set as the first computation result.