PURPOSE: To increase an outside-band attenuating amount in the both areas of a filter characteristic, and to improve the filter characteristic by making the hardness of adhesive through with a piezoelectric board is adhered to a substrate more than a specific value.

CONSTITUTION: This part is equipped with a substrate 5, piezoelectric board l fixed through adhesive 4 to the substrate 5, and input and output electrodes 2 and 3 provided on the surface of the piezoelectric board 1. The hardness of the adhesive is more than 95 in a Rockwell hardness testing method described in a JISK7202. That is, while the outside-band attenuating amount in the both areas of the filter characteristic can be less than 45dB by the adhesive 4 whose hardness is less than 80 in the Rockwell hardness testing method, the outside- band attenuating amount can be more than 50dB by the adhesive whose hardness is more than 95 in the Rockwell hardness testing method. Thus, the filter characteristic can be extremely satisfactory.