To obtain a measuring method in which the bending rigidity of an already constructed structure is measured simply without being influenced by a boundary condition which expresses the support state of the structure.

A measuring method for the bending rigidity EI of a structure 10 uses a relationship in which the propagation speed of a bending vibration propagated in the structure 10 is decided according to the bending rigidity EI of the structure 10. In the measuring method, a shock is given to the structure 10, traveling waves of a bending vibration due to its shock are detected by a vibration sensor 21 and a vibration sensor 22 which are arranged on the structure 10, they are analyzed in accordance with frequency, and the phase difference between the two sensors 21, 22 is obtained for every frequency. The phase difference correspondings to the time in which the bending vibration is propagated between the two sensors 21, 22, i.e., to the propagation speed of the bending vibration. Then, the bending rigidity EI of the structure 10 is calculated on the basis of a set relationship which is established between the phase difference obtained in this manner and the bending rigidity EI of the structure 10.