A surface acoustic wave (SAW) resonator, including: a first interdigital
transducer composed of a pair of interdigital electrodes provided in a
propagation direction of a surface acoustic wave; a second interdigital
transducer composed of a pair of interdigital electrodes provided in
parallel to the first interdigital transducer; and a switch that
alternately switches the pair of interdigital electrodes of the first
interdigital transducer and the pair of interdigital electrodes of the
second interdigital transducer; wherein
7.lamda..ltoreq.B.ltoreq.33.lamda. where .lamda. is a wavelength of a
surface acoustic wave, and B is an addition of a width a1 of an engaged
section of electrode fingers of the first interdigital transducer, a
width a2 of an engaged section of electrode fingers of the second
interdigital transducer, and a distance b between the engaged sections of
both interdigital transducers.