Abstract: An ultrasonic testing device of the type comprising a fixed hub with at least one ultrasonic transducer as well as an annular rolling means mounted for rotation on said hub and surrounding said transducer, this latter being mounted on the hub through a support whose external face opposite said transducer defines with the inner face of said rolling means a rotational sliding slit, the coupling between said support and said rolling means being provided by an ultrasonic liquid present in said slit, wherein a spongy resilient element is provided imbibed with said coupling liquid, said element being housed in a recess in said hub and being applied resiliently against the inner face of said rolling means.