PURPOSE: To receive sound waves with high output stability without being affected with longitudinal external pressures by arranging a 1st and a 2nd piezoelectric layers continuously in the axial direction of a cable and making the hydrophone coefficients of both of the layers differ from each other.

CONSTITUTION: A 1st piezoelectric layer 2 is formed with a material of a larger hydrophone coefficient and its inner and outer sides are polarized respectively to positive and negative poles. A 2nd piezoelectric layer 3 is formed with a material of a smaller hydrophone coefficient and its inner and outer sides are polarized respectively to negative and positive poles. When a piezoelectric cable receives a longitudinal external pressure, electric charges are produced in the layers 2 and 3. The amounts of the charges, however, are equal to each other and a positive and negative poles are shorted and the polarity is eliminated so that no potential difference is produced between output terminals 12 and 13. When the cable receives a sound wave on the other hand, since the hydrophone coefficient of the layer 2 is larger than that of the layer 3, an output corresponding to the sensitivity difference is produced between the terminals 12 and 13. In this way, effect of external pressure is eliminated and the sound wave is received with a high output and stability.