PURPOSE: To compact a piezo-electric electro-acoustic converter or to attain in high sound pressure or band expansion to the low frequency side without changing the size of the converter by forming a case by a conductive thin plate, sticking a piezo-electric ceramic plate to the case and allowing the whole case to act as a resonator.

CONSTITUTION: A piezo-electric ceramic plate 2 forming electrodes on both the main faces is stuck to the center flat part of a case 21 formed by bending and molding the peripheral edge part of a brass plate. A cover body 22 formed by a brass thin plate is stuck and fixed to the peripheral edge part of the case 21 so that an acoustic space 23 is formed on the opposite side of the case 21 opposed to the plate 2 and the lower face of the cover body 22 is fixed to a base by means of a pressure sensitive adhesive double coated tape or the like. In the constitution, one of spaces formed on both the sides of a convensional piezo-electric diaphragm can be removed, the whole case 21 is constituted so as to act as a resonator and the size of the whole converter can be compacted.