To provide an apparatus and a method of determining the degree of damage of a building capable of quickly determining the degree of damage of the building in a simple and inexpensive manner.

The method includes steps of measuring an acceleration response of a building due to seismic waves by an acceleration sensor 21, calculating a running spectrum by means of the acceleration response by a spectrum analysis means 43, evaluating a predominant period where amplitude takes its peak value for each of acceleration response spectra in respective time intervals in the running spectrum by a predominant period extracting means 44, evaluating the longest period among the predominant periods of the respective time intervals by a longest period determining means 45, estimating a distortion angle of the building by means of the longest period by a distortion angle computing means 46, determining the degree of damage of the building depending on the size of the distortion angle by a processing means 47 for determining the degree of damage of a building, and outputting the determination results to an external output device 30.