PURPOSE: To secure a relative attenuation quantity of the high-range side image frequency of an IF center frequency above 72-75dB by specifying the metallization ratio of the IDT electrode of a SAW resonator at a value larger than 0.68.

CONSTITUTION: An IDT(interdigital electrode transducer) 10 is provided on a quartz substrate and its metallization ratio L1/L is ≥0.68, where the length L1 is equal to IDT finger width, light L is λ/2, and a gap 20 is L-L1. The relative attenuation quantity of an image point that the SAW(surface acoustic wave) resonator filter needs to have varies among set makers, but is generally 72-75dB. To obtain the relative attenuation quantity of the image point above 75dB, the finger width L1 is only set to ≥8.2μm (equivalent to mtallization ratio L1/L≥0.68). The upper limit of the ratio L1/L is raised on condition that fingers 10 have no mutual short circuiting consideration of the precision of photolithography.