DEFECT DETECTION DEVICE AND DEFECT DETECTION METHOD

In a defect detection device (10), an exciter (11) gives a test object (S) a vibration with a variable frequency. A vibration state measurer (15, 163) performs a measurement of the vibration state of the surface of the test object by an optical means while the vibration is given to the test object, and determines, for each position on the surface, a numerical value representing the vibration state based on a result of the measurement. A judgment-index-value determiner (164) determines a judgment index value by Fourier transform based on the numerical value representing the vibration state at each position, where the judgment index value is a numerical value representing a strength of the vibration for each wavenumber. A wavenumber-wavelength determiner (165) determines, based on the judgment index value determined for each wavenumber, a wavenumber or wavelength of an elastic wave induced in the test object by the vibration.