PURPOSE:To minimize the effects of a mechanical distortion of the holder and thermal distortion due to the difference of a linear expansion coefficient between a holder and a piezoelectric substrate, by applying a voltage to an electrode formed on the surface, for bonding a rear center of a piezoelectric body performing electric signal processing to the surface center of the holder. CONSTITUTION:A bonding section is provided at a part of the rear center of the piezoelectric substrate 2 and bonded to the holder 1. Thus, the shift in the center frequency and th deterioration in the ageing characteristic produced because of the deformation of the holder considered to take place most probably at the sealing as shown in Fig. (b) are prevented. But the piezoelectric substrate 2 is subject to distortion with the deformation of the holder 1 as shown in Fig. (c). Then, the piezoelectric substrate 2 is bonded to a projection 7 of the holder 1 having the projection 7. Thus, the distortion due to the mechanical stress produced at sealing caused on the piezoelectric substrate 2 is prevented.