Defect inspection device and defect inspection method

A defect inspection device comprising:

• an excitation unit that excites an elastic wave in an inspection target;
• a control unit that acquires vibration state information which is information about a state of the elastic wave excited in the inspection target for a plurality of frequencies by changing a frequency of excitation vibration caused by the excitation unit in order to excite the elastic wave in the inspection target, and extracts recommended frequencies recommended for inspecting a defect of the inspection target from among the plurality of frequencies based on the acquired vibration state information for the plurality of frequencies;
• an irradiation unit that irradiates a measurement region of the inspection target with laser lights in a state of exciting the elastic wave in the inspection target by the excitation unit;
• and
• a measurement unit that causes the laser lights reflected in the measurement region to interfere with each other by a laser interference method, and measures the interfered laser lights.