The defect inspection device is provided with a sound wave excitation unit for exciting a sound wave having a time waveform represented by a continuous periodic function to a prescribed position on the surface of an object to be measured, a displacement amount measurement unit for measuring a periodically varying displacement amount generated by the propagation of the sound wave from the prescribed position through the surface at at least three different phases of the periodic variation, and a periodic function acquisition unit for determining a periodic function expressing the periodic variation of the physical quantity on the basis of the displacement amount at the at least three different phases.