PURPOSE: To secure the control for the frequency characteristics by detecting and then feeding back the vibrations of the telephone receiver, thus enhancing the articulation of the bone condution hearing aid.

CONSTITUTION: Vibration bar 22 of the bone receiver is supported by spring 23, and the adjustment is given via spacer 24 between pole pieces 19 and 22. Vibration transmission part 25 is fixed to spring 23 along with pole piece 22, and capacitor is formed between pieces 22 and 19. The charged electret film 26 is adhered close to piece 22 so that the overlap voltage of the capacitor may vary when piece 22 has vibrations. And the overlap voltage receives such phase with which the negative feedback may be satisfied near the resonance frequency via the phase circuit, and is then fed back to the amplifier. Thus only the frequency characteristics near the resonance frequency is improved from 27∼29 as shown in the graph.