For the optimal control problem of an active dynamic vibration absorber (active DVA), this paper considers optimal control using a reduced-order model and three kinds of output feedback controls: the acceleration, velocity and displacement feedbacks of a main structure, adding together the displacement and velocity feedbacks of an active DVA. A unified approach for the optimization of the various controls of the active DVA for multidegrees-of-freedom systems is presented by identifying these as an optimization problem with control structure constraints. By carrying out numerical calculations and experiments, the characteristics of those controls were investigated and the usefulness of the present method was demonstrated.