To measure easily and accurately rigidity of each part of a car body, and to facilitate evaluation and management of the rigidity of each part.

The periphery of a disposal part of an accelerometer is hammered and excited by an impact hammer, and the force at that time is detected, and an acceleration from the accelerometer is measured, and a frequency response function is measured. Then, each measured value in a frequency domain set beforehand is decomposed into each vibration mode relative to the measured frequency response function, and re-synthesized, and curve-fit processing is performed to be approximated by a correct waveform. Each frequency response function of each measured value in the frequency domain set beforehand is subjected to modal analysis one by one by the curve-fit processing, to thereby determine a modal parameter. Then, a value of each decomposed vibration mode at 0 Hz is estimated, and the values are synthesized, to thereby determine vibration displacement at 0 Hz as a reciprocal of the rigidity.