This paper presents a response evaluation method for a seismic control structure includes a large weight sub-system as dynamic mass damper. Not only a conventional 2-element sub-system but also a 3-element sub-system with an inertial mass are taken into consideration. The fundamental idea is to consider the main-system’s displacement as that of equivalent SDOF system, and the sub-system’s stroke as a modified independent sub-system’s displacement amplified by the interaction with the main-system. First, optimum absorber parameters of variable conditions are derived. After formulating the needed equations for evaluation, the accuracy of the method are discussed by numerical analyses.
