A strength testing method of testing, for a tensile strength, a test body that is a fiber reinforced composite material, the method comprising: applying a tensile load to the test body during a test period so as to increase as time elapses, and detecting, at each time point, by an AE sensor, a vibration displacement of an AE wave generated in the test body by the tensile load; generating, based on the vibration displacement of an AE wave detected at each time point, for each of a plurality of time sections, waveform data that represent a vibration displacement of the AE wave at each time point, wherein the plurality of time sections constitute the test period and each have a length of time; and for each of the plurality of time sections, transforming the waveform data into spectrum data that represent an intensity of the AE wave at each frequency; specifying, for each of the plurality of time sections, a peak of an intensity in the spectrum data; extracting, for each of the plurality of time sections, processing target data that are included in the spectrum data and in which an intensity is equal to or higher than a value of a set percentage of the peak, wherein the processing target data is a part of the spectrum data; for each of the plurality of time sections, performing transform on the processing target data from data of an intensity with respect to a frequency into processing target time data of an intensity with respect to time; concerning each of the plurality of time sections, for each of a plurality of subsections, transforming the processing target time data in the subsection into spectrum data of an intensity with respect to a frequency, and determining a frequency center (Fg) of gravity of the AE wave for the transformed spectrum data in the subsection, wherein the plurality of subsections constitute the time section and each have a length of time; concerning each of the plurality of time sections, specifying, as a most frequent value of the frequency centers (Fg) of gravity, the frequency center (Fg) of gravity that is among the frequency centers (Fg) of gravity of the plurality of subsections included in the time section and that most frequently appears; and outputting strength evaluation data for evaluating a tensile strength of the test body, wherein the strength evaluation data are data in which the most frequent value for each of the plurality of time sections is associated with a tensile load applied to the test body in the time section. applying a tensile load to the test body during a test period so as to increase as time elapses, and detecting, at each time point, by an AE sensor, a vibration displacement of an AE wave generated in the test body by the tensile load; generating, based on the vibration displacement of an AE wave detected at each time point, for each of a plurality of time sections, waveform data that represent a vibration displacement of the AE wave at each time point, wherein the plurality of time sections constitute the test period and each have a length of time; and for each of the plurality of time sections, transforming the waveform data into spectrum data that represent an intensity of the AE wave at each frequency; specifying, for each of the plurality of time sections, a peak of an intensity in the spectrum data; extracting, for each of the plurality of time sections, processing target data that are included in the spectrum data and in which an intensity is equal to or higher than a value of a set percentage of the peak, wherein the processing target data is a part of the spectrum data; for each of the plurality of time sections, performing transform on the processing target data from data of an intensity with respect to a frequency into processing target time data of an intensity with respect to time; concerning each of the plurality of time sections, for each of a plurality of subsections, transforming the processing target time data in the subsection into spectrum data of an intensity with respect to a frequency, and determining a frequency center (Fg) of gravity of the AE wave for the transformed spectrum data in the subsection, wherein the plurality of subsections constitute the time section and each have a length of time; concerning each of the plurality of time sections, specifying, as a most frequent value of the frequency centers (Fg) of gravity, the frequency center (Fg) of gravity that is among the frequency centers (Fg) of gravity of the plurality of subsections included in the time section and that most frequently appears; and outputting strength evaluation data for evaluating a tensile strength of the test body, wherein the strength evaluation data are data in which the most frequent value for each of the plurality of time sections is associated with a tensile load applied to the test body in the time section.