PURPOSE: To increase the resistance to the mechanical shock or vibration and to prevent the effect of moisture, etc., by holding a spacer between the layers of an edge mode ceramic filter and then immersing the filter in a low temperature molten material and then in the porous thermosetting resin.

CONSTITUTION: Three units of element in which lead terminals 2", 3" and 4" are connected to an input terminal 2', an earth terminal 3' and an output terminal 4' respectively are held by a holder 10 so as to secure nearly the same space between the piezoelectric ceramic plates 1 and then stacked to each other in the direction of thickness. Then a spacer 7 is held between the layers at the vibrating area. Thereafter, the elements are immersed in a low temperature molten material that is turned into a solid or semisolid at the normal temperature and up to the position of about 1.5 times as much as the width of the plate 1 from the tip of the plate 1, and then the 1st coated layer 8 is put over the element. Furthermore the 2nd resin coated layer 9 is formed on the outside of the layer 8 by immersing the holder 10 plus the terminals 2", 3" and 4" in the porous thermosetting resin and heating and hardening the resin. Thus the layer 8 is absorbed to form a microspace.