An ultrasonic transmitter 3 attached to an inspecting target object 1, an ultrasonic receiver 5 receiving a reflected wave of the ultrasonic wave that has propagated from the ultrasonic transmitter 3 in the inspecting target object, a data processing device 7 acquiring position specifying data for specifying a position of a defect 1a in the inspecting target object 1 on the basis of received data representing a waveform of the reflected wave received by the ultrasonic receiver 5 are provided. The ultrasonic wave generated by the ultrasonic transmitter 3 has been frequency-modulated, and has a waveform composed of components of respective frequencies that are deviated from a resonance frequency of the ultrasonic transmitter 3 and the ultrasonic receiver 5. The data processing device 7 includes a pulse compressing unit 21 performing pulse compression on the received data, and acquires the position specifying data on the basis of the pulse-compressed received data.