To provide a method of evaluating structural soundness which dispenses with a prior vibration test of the structure to be evaluated, and further which excels in the reliability of the obtained results.

The natural frequency f1 (Hz) of a structure and the natural frequency f2n (Hz) of the structure with n conditions, when masses mn (kg) different from one another where n is a natural number are loaded on the structure are calculated, based on vibration data detected by applying vibration to the structure. Then, the mass of the structure during evaluation is estimated, based on the natural frequency f1and the natural frequency f2n which are calculated, the masses mn loaded to the structure, and equation (1). M in equation (1) refers to an estimation value of the mass of structure during the evaluation. Then, flexural rigidity of the structure during the evaluation is calculated, based on the estimated mass of the structure, and it is regarded as an evaluated value. Then, the soundness of the structure is evaluated based on the evaluated value.