A device is provided for the ultrasonic measuring of cylindrical test specimen, in particular tubes and hoses, wherein said device can be filled with water or submerged in a water bath and is provided with at least one ultrasonic measuring head secured on the device. The device is characterized by a cylindrical reference mandrel, the longitudinal axis of which at least essentially coincides with the measuring axis of the device, and at least one cylindrical auxiliary mandrel that extends parallel to the reference mandrel, can be moved to a position between the ultrasonic measuring head and the reference mandrel, and can also be removed from this position.