Abstract: A ultrasonic device for non-destructive testing of thin tubes, for instance heat exchanger tubes, comprises a head having a longitudinal axis and insertable into a tube. A mechanism imparts to the head a rectilinear motion along and a rotational motion about the axis. The head contains ultrasonic transducers coupled with the tube through a fluid and able to transmit an ultrasonic beam in the form of volume waves in a direction at an angle with the longitudinal axis and to detect echoes. The transducers include one (or more) ultrasonic transducer delivering a focussed beam directed in a plane containing the longitudinal axis and at an angle with a direction perpendicular to the longitudinal axis, and one (or more) second ultrasonic transducer delivering a focussed beam parallel to a line perpendicular to the longitudinal axis and located at a distance from the line. Circumferential as well as longitudinal flaws may consequently be detected.