To detect the oscillation characteristic of a structure effective in improvement of determination accuracy and rapid evaluation determination of the earthquake-affected degree of the structure.

This oscillation characteristic detecting method includes a step of detecting input wave to the structure A by seismic ground motion and response wave of the structure A, a step of dividing the input wave and response wave into segments every predetermined time, and a step of determining the oscillation characteristic hysteresis of the structure having undergone the seismic ground motion based on the oscillation characteristic identified for each segment. In this method, since the oscillation characteristic is identified for each segment, the oscillation characteristic of the structure indicating a nonlinear behavior can be obtained with a plurality of divided and obtained equivalent linear oscillation characteristics. As a result, the oscillation characteristic of the structure A effective in improvement of the determination accuracy of the earthquake affected degree of the structure A can be detected.