An ultrasound flaw detection device which detects abnormalities within a tube while moving in the tube by pressure of water flow. The ultrasound flaw detector includes an ultrasound probe (11) which emits an ultrasound wave from an inside of the tube to a tube wall and receives an echo signal, a pulser-receiver (12) which transmits a pulse signal to the ultrasound probe and to which the received echo signal is inputted, a memory unit (14) which stores the received echo signal, a control unit (15) which controls transmitting timing of the pulse signal from the pulser-receiver to the ultrasound probe and controls writing of the received echo signal to the memory unit, and a power supply unit (19); a flexible member (25) which connects the plurality of parts of the ultrasound flaw detector; and a centering member (26) which keeps the ultrasound probe approximately centered within the tube.