A coating film is formed on the whole surface area of a body part. Formation of the coating film may be done by immersing the body part in a solution of parfluoropolyether. Then, the parfluoropolyether constituting the coating film is joined with the side surfaces of the body part by irradiating Xenon excimer laser in a nitrogen atmosphere onto the side faces of the body part, or to the surface exposing an electrode layer. As a result, the protective film is formed only on the side surfaces of the body part. Thus, the protective film is formed as a monomolecular film. Total body part is then cleaned by 2,3-dihydrodecafluoropentane to remove non-reacted coating film, thereby completing a multi-layer piezoelectric element.