Abstract: A tube flaw detecting method detects a flaw portion in a heat exchanger tube constituting a boiler furnace wall using two probes, enabling one to carry out appropriate inspection work with a high efficiency. A transmitter probe and a receiver probe are juxtaposed in a circumferential direction, and an ultrasonic wave is transmitted from the transmitter probe to propagate. Repeated reflections occur at a tube inner surface and tube outer surface, and the wave is reflected at a crack extending in the circumferential direction to return, propagating likewise to be received by the receiver probe so that existence of the crack is confirmed. Thus, inspection work for a crack can be done with certainty with a simple arrangement.