PROBLEM TO BE SOLVED: To provide an ultrasonic flaw detection method which can obtain a correct cross-sectional image of a defect in a subject even when the surface of the subject is inclined from the original position.SOLUTION: In an ultrasonic flaw detection method for obtaining an image including a defect in a subject 1 by scanning an oscillation ultrasonic wave in a constant direction with a prescribed incidence angle &thetas; maintained with respect to the surface of the subject 1 from an ultrasonic transceiver 2, and overlapping images at respective scanning positions obtained from reflection ultrasonic waves received by the ultrasonic transceiver 2 in respective scanning in which the incidence angle &thetas; is changed, a distance L from the ultrasonic transceiver 2 at each scanning position to the surface of the subject 1 is calculated with the reflection ultrasonic wave, and the respective images obtained at the respective incidence angles are displaced and overlapped so as to offset errors &Dgr;Z, &
