PURPOSE: To prevent interdigital electrodes from being damaged due to the pyroelectric effect by short-circuiting the interdigital electrodes when an electrode pattern is formed.

CONSTITUTION: A pattern 7 connecting a 1st stage and a 2nd stage is connected to a reflector 4a via an adjacent ground short-circuit pattern 8 for an electrode group with a signal short-circuit pattern 9a. A signal side of middle interdigital electrodes 3b, d is connected to the reflector via bonding pads 6a, d and the pattern 8 by the pattern 9b. Then adjacent electrode groups are connected respectively similarly. Thus, discharge due to the pyroelectric effect is prevented in the electrode pattern forming process and an excellent out-band attenuation is obtained by 2-stage of cascade connection. Thus, damages to interdigital electrodes due to the pyroelectric effect are prevented in the planer structure in which interdigital electrodes are connected in parallel with each other on a piezoelectric substrate.