PURPOSE:To improve inspection capacity by making ultrasonic waves incident from plural places to the inside of a material or a structural material, receiving the reflected waves in plural places, determining the position, shape, size and number of the defects in the structural material from the time and waveforms of the transmitted and received ultrasonic waves by arithmetic processing and displaying the same. CONSTITUTION:The 1st transmitting and receiving element is put to the on state in which ultrasonic transmission is possible and n-pieces of pulses for generating ultrasonic waves are impressed to an ultrasonic wave transmitter and receiver 23. The pulses are made incident through a circuit 22 for switching ultrasonic wave transmitter and receivers to a circular cylindrical steel material 30. A waveform storage circuit 24 transmits the stored ultrasonic wave signal to a preprocessing circuit 25 by the transfer signal from a control circuit 21 and feeds the signal for the utrasonic wave transmission and reception time and the peak value of the waveform to an arithmetic processing circuit 26. Said circuit makes the calculation to determine ellipse from the received data and the data on the transmitting and receiving element position from an input circuit 27. The result is stored in a memory. The defect distribution in the structural material is thus easily obtd. and since the display of the section is possible, the decision of the size and shape of the defect is made possible.