A bonded body includes a supporting body composed of a ceramic, a bonding layer provided over a surface of the supporting body and composed of one or more material selected from the group consisting of mullite, alumina, tantalum pentoxide, titanium oxide and niobium pentoxide, and a piezoelectric single crystal substrate bonded with the bonding layer. The surface of the supporting body has an arithmetic average roughness Ra of 0.5 nm or larger and 5.0 nm or smaller.