A bonded body includes a supporting substrate composed of a polycrystalline ceramic material or monocrystalline material, a piezoelectric single crystal substrate and a bonding layer provided between the supporting substrate and piezoelectric single crystal substrate. The bonding layer has a composition of Si(1-x)Ox (x represents an oxygen ratio). The oxygen ratio is increased or decreased from an end part of the bonding layer on the side of the piezoelectric single crystal substrate to an end part of the bonding layer on the side of the supporting substrate. The maximum value of the oxygen ratio x in the bonding layer is 0.013 or higher and 0.666 or lower, and the minimum value of the oxygen ratio is 0.001 or higher and 0.408 or lower.