An ultrasonic testing method, comprising: a disposing step of disposing an ultrasonic probe (1, 1A, 1B, 1C, 1D) including n (n ≥ 2) number of transducers (11-1,..., 11-64) arranged along a predetermined direction so as to face a test object; a testing step of testing the test object by selecting m (n > m ≥ 1) number of transducers from among the n number of transducers (11-1,..., 11-64), transmitting ultrasonic waves from the selected m number of transducers toward the test object and receiving the ultrasonic waves therefrom; and a scanning step of switching m number of transducers to be selected successively, the method repeating the testing step and the scanning step alternately, thereby ultrasonically testing the test object, wherein, in the scanning step, if an angle that the arrangement direction of the n number of transducers (11-1,..., 11-64) makes with the surface of the test object which ultrasonic waves enter is θ(°), and the effective beam width of each selected m number of transducers with respect to a target flaw is W1 (mm), m number of transducers to be selected are switched successively by a switching pitch length P (mm) satisfying the following formula: P ≤ W 1 ⋅ cosθ in the testing step, the test object is tested with testing sensitivity adjusted beforehand for each selected m number of transducers (11-1,..., 11-64) so that the highest echo intensities from target flaws received by each selected m number of transducers (11-1,..., 11-64) are approximately equivalent, and the effective beam width of each selected m number of transducers with respect to a target flaw indicates a length of a range in which flaw echo intensity is not lower than a predetermined intensity in the profile of echo intensity from the target flaw that is obtained when each selected m number of transducers is scanned in the transducers arrangement direction. a disposing step of disposing an ultrasonic probe (1, 1A, 1B, 1C, 1D) including n (n ≥ 2) number of transducers (11-1,..., 11-64) arranged along a predetermined direction so as to face a test object; a testing step of testing the test object by selecting m (n > m ≥ 1) number of transducers from among the n number of transducers (11-1,..., 11-64), transmitting ultrasonic waves from the selected m number of transducers toward the test object and receiving the ultrasonic waves therefrom; and a scanning step of switching m number of transducers to be selected successively, the method repeating the testing step and the scanning step alternately, thereby ultrasonically testing the test object, wherein, in the scanning step, if an angle that the arrangement direction of the n number of transducers (11-1,..., 11-64) makes with the surface of the test object which ultrasonic waves enter is θ(°), and the effective beam width of each selected m number of transducers with respect to a target flaw is W1 (mm), m number of transducers to be selected are switched successively by a switching pitch length P (mm) satisfying the following formula: P ≤ W 1 ⋅ cosθ in the testing step, the test object is tested with testing sensitivity adjusted beforehand for each selected m number of transducers (11-1,..., 11-64) so that the highest echo intensities from target flaws received by each selected m number of transducers (11-1,..., 11-64) are approximately equivalent, and the effective beam width of each selected m number of transducers with respect to a target flaw indicates a length of a range in which flaw echo intensity is not lower than a predetermined intensity in the profile of echo intensity from the target flaw that is obtained when each selected m number of transducers is scanned in the transducers arrangement direction.