To secure stable operation of an active type damping device with an effective phase shift-adaptive control.

An active damping system 10 uses the phasor technique suited to an excessive phase shift of constituting elements of the system and uses an optimum control technique for determining a preliminary value of a model of a controller. The preliminary coefficients are scale-processed so as to indicate the difference of a unit, and the scale-processed coefficients are used for determining a phase angle and the relative size of the phasor. Relating to the respective components of control force to a tuned mass 24, respective phasors are suited to already known phase shift in the system and displaced so as to hold the same relative size of the phasor relating to the respective components. A phase shift coefficient value is scale-processed so as to return the coefficient to an original unit, the coefficients are used in the controller, command signals are generated and external force 28 for adjustment is added to the tuned mass 24.