PURPOSE: To prevent the remaining of deformation at the time of parting of a cap having a jaw part for preventing pull off and to assure the sure fitting of a base and the cap by molding this cap of a resin, then heat treating the cap and fitting the cap to the base after cooling.

CONSTITUTION: The cap 4 having the jaw part 14 for preventing pull off is molded of the resin and is heat treated. After this cap is cooled, the cap is fitted to the base 3. The cap 4 after the molding is heat treated and is cooled down to ordinary temp., by which the bore D in the aperture is made into the value nearly equal to the prescribed design value. The base 3 and the cap 4 are thus surely fitted and the piezoelectric sounder which is hardly disengageable is obtd. The base and the cap are surely fitted to each other in this way without allowing the deformation of the cap at the time of parting from the mold to remain.