PURPOSE: To improve the adhesion between a piezoelectric element substrate and a diaphragm, by bonding the diaphragm and the piezoelectric element substrate, through the use of a soft force of compressed gas and the elasticity of the diaphragm.

CONSTITUTION: One side of a ceramic piezoelectric element substrate 11 having electrode 11a and 11b on both major planes is applied with an adhesives 12 and the opposite side is adsorbed with a vacuum adsorbing tool 14. On the other hand, a diaphragm 15 is held with another vacuum adsorbing tool 16 and arranged to the substrate 11 opposingly. When the diaphragm 15 is adsorbed, the center is externally bent so that the center is projected. The diaphragm 15 is fallen down until the tip contacts the plane applied with the adhesives 12 and stopped while weakening the vacuum adsorbing force of the tool 16, allowing to bond the diaphragm 15 to the substrate 11 from the center to the circumference sequentially with the restoring force of the plate 15 itself. In this case, compressed gas is given to the tool 16 via a gas blowing section 16b and blown on the plane of the diaphragm 15. The vacuum adsorbing force of the substrate 11 is removed and the adhesives 12 is cured.