Abstract: An electrical signal transfer element is disclosed. This element consists of a ultrasonic wave solid propagation medium, input and output transducers and backing members. The ultrasonic wave solid propagation medium has a ultrasonic wave propagation distance which is shorter than a distance between main surfaces or a distance between side surfaces. The input and output transducers attached to ultrasonic wave signal input and output surfaces of the foregoing propagation medium serve to convert an input electric signal into a ultrasonic wave and to convert this ultrasonic wave into an output electric signal. The backing members are joined to surfaces opposite to joint surfaces of the input and output transducers to the propagation medium.