The aim of this study is to propose a new output-only system identification technique using a virtual 1-DOF mass tuner(VMT) which is analogous to the tuned mass damper and has a characteristics to amplify the response of the measured acceleration responses of building structure. The VMT is a kind of modal filter that its response is maximized in the range of the natural frequency of a structure, and damping ratio of the structure can be identified using the response ratio of VMT at the different damping ratios consisting the VMT. Also, it is shown that the modal parameters can be precisely estimated if the VMT were applied to the mode response separated with mode decomposition method in the state space. For the verification of the proposed technique, the identification process is applied to the measured acceleration responses from 40 story steel frame structure when typhoon approached to the building. From the numerical simulation, it is found that the modal responses are well separated in the state space, the modal parameters are precisely identified with the proposed modal property estimation method.