To identify structure of a structure by oscillating the structure.

A value of a variable element, a natural frequency of a tested object varied in response thereto and a vibration characteristic of a characteristic vector or the like are measured by a sensor attached to the tested object, in the tested object built in with an oscillation part for oscillating the tested object, and the variable element variable in an inertia characteristic. A measured vibration characteristic and the measured value of the variable element are read into a computing part to constitute a linear matrix equation to identify a structure matrix including an unknown structure parameter of the tested object, excepting the variable element. Then, the linear matrix equation is solved as to the unknown structure matrix to calculate the unknown structure matrix.