Ultrasonic thickness reduction inspection method/apparatus

An ultrasonic thickness reduction inspection apparatus, comprising:

• a plurality of ultrasonic sensors disposed on a surface of an inspection target;
• a transmitter/receiver configured to excite the plurality of ultrasonic sensors by a frequency modulated wave signal in which a frequency is changed with time, to supply ultrasonic waves to an inside of the inspection target, and to receive signals in which the plurality of ultrasonic sensors is excited by a plurality of echoes from the inside of the inspection target by the ultrasonic waves supplied to the inside of the inspection target;
• and
• a signal processor/recorder configured to sum the plurality of echo signals received by the transmitter/receiver, to calculate a time difference between a first peak of the summed signal and a first peak of the frequency modulated wave signal from cross correlation between signals summing the plurality of echo signals and the frequency modulated wave signal, and to detect a change in a thickness of the inspection target based on the calculated time difference.