PROBLEM TO BE SOLVED: To evaluate flaw detection skill of a flaw detection technician by detecting flaws of a testpiece having a lot of straight grooves provided in its bottom by ultrasonic waves and automatically compensating and displaying a reference flaw detecting wave height read from a database. SOLUTION: A testpiece 20 has no other material defects except for straight grooves. The material defects are stored in a database as a reference flaw detection waveform data and are distributedly arranged in an area equivalent to a flaw detection face of the testpiece 20 as virtual detects in software. A flaw detection technician reads out position coordinates of a probe 11 as the address of the reference flaw detection waveform data, scans it for a flaw detection while watching the waveform displayed on a display 34, and stores the defect echo height in a data storage processing device 33 based on the flaw detection waveform data. When the reference flaw detection waveform is displayed on the display 34 and the detect echo height is stored, the change component should be compensated so that the echo height from the straight grooves is utilized as its compensation data in this device.