The ultrasonic flaw detection method according to the present invention includes a step of disposing an ultrasonic probe 1 having a plurality of transducers 11 so as to face a tubular flaw detection material P, and a propagation direction of ultrasonic waves in the tubular flaw detection material. Selecting an appropriate transducer from the plurality of transducers such that the ultrasonic waves are transmitted and received in a plurality of different propagation directions, and the outer surface refraction angle θr of the ultrasound in the plurality of propagation directions is The flaw detection conditions by the ultrasonic probe are set so as to be substantially equal to each other and / or so that the inner surface refraction angles θk of the ultrasonic waves in a plurality of propagation directions are substantially equal to each other. .
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