Proposed is a modification coefficient which is to be multiplied to earthquake response spectra with 5% damping ratio of critical to obtain response spectra of arbitrary damping ratio h. A modification coefficient ξ_SA was defined as S_A(T, h)/S_A(T, 0.05) in which S_A(T, h) represents absolute acceleration response spectral amplitude for natural period T and damping ratio h. Studied was a variation of ξ_SA in accordance with natural period T and frequency characteristics of ground motions represented in terms of acceleration response spectral ratio β(T, 0.05) (β=S_A(T, 0.05)/a_max, in which a_max represents the peak acceleration). Horizontal strong motion records of 206 components obtained at free field sites in Japan were used for the analysis. It was concluded that coefficient ξ_SA can be approximated as 1.5/(40h+1)+0.5.