Provided are an ultrasonic testing method and an ultrasonic testing apparatus capable of accurately detecting flaws present in a weld zone of a test object, such as a welded pipe, regardless of the position of the flaws. An ultrasonic testing apparatus 100 includes an ultrasonic probe 1 which is provided with n (n≧2) transducers 11 arranged along a direction orthogonal to the weld line of a weld zone P1 of a test object P and is arranged so as to face the weld zone, and transmission/reception control means 2 which selects m (n>m≧1) transducers from the n transducers, causes the selected transducers to transmit and receive ultrasonic waves to and from the weld zone, and switches the selected transducers one after another. The transmission/reception control means switches the selected transducers one after another so that the range of an effective beam width of each of the selected transducers that have been switched for a flaw to be detected has an overlapping portion, and in the transmission/reception control means, the flaw detection sensitivity is adjusted beforehand for each of the selected transducers so that maximum echo intensities from a flaw to be detected, which are each received by each of the selected transducers that have been switched, become substantially equal to each other.