Abstract: A leakage-sound detecting apparatus is provided for efficiently detecting water leakage in a plastic pipe by increasing sensitivity to a low frequency sound component and efficiently reducing stray noise, as well as protecting a piezoelectric element. To this end a detection portion and a pedestal portion are connected through a mechanical resonant member formed of a soft material. A low frequency sound component is amplified by the resonant member, and high frequency components are substantially attenuated. In an alternative arrangement a detection portion and a mechanical resonant member mounted on a pedestal portion are connected through a buffer portion having a buffer member arranged therein. When a shock is applied to the bottom of the pedestal portion, due to the apparatus being dropped for example, the buffer member is compressed, and no overload is applied to a piezoelectric element.