We have proposed to define structural damage measures in terms of global stiffness parameters wi. and offered a set of damage indicator D_w,i. However, applying this concept a question arises how many indicators D_w,i should be considered. In this paper we apply the improved damage indicator using the Effective Mass Ratio (EMR) or Modal Contribution Factor(MPF). By means of the new damage indicator considering the participation ratio of each eigen-mode, we can get a unique value as a damage index. Three numerical examples demonstrated the applicability of this new damage indicator.