A bonding layer 3 is formed over a piezoelectric material substrate, and the bonding layer 3 is made of or more material selected from the group consisting of silicon nitride, aluminum nitride, alumina, tantalum pentoxide, mullite, niobium pentoxide and titanium oxide. Neutralized beam A is irradiated onto a surface 4 of the bonding layer and a surface of a supporting body to activate the surface of the bonding layer and the surface of the supporting body. The surface of the bonding layer and the surface of the supporting body are bonded by direct bonding.