A plate material 1 and piezoelectric ceramics 2 are bonded together through an alloy layer 3 formed by an alloy forming reaction due to the mutual diffusion phenomena between a liquid metal including at least galium and the plate material 1 or the piezoelectric ceramics 2, or the mutual diffusion phenomena between the liquid metal and metal powder. The alloy layer 3 may include at least one or more of indium, tin and zinc and at least one or more of copper, silver, gold, and palladium. Further, a metal may be provided on at least one of the bonded surfaces of the plate material 1 and the piezoelectric ceramics 2. This metal may include one or more of copper, silver, gold, tin and palladum. In addition, a metal layer may be formed on the bonded surface 1a side of the plate material 1. Still further, an amorphous layer may be formed on at least one of the parts between the plate material 1 and the alloy layer 3, and between the piezoelectric ceramics 2 and the alloy layer 3.