A surface acoustic wave resonator, a filter and a communication device are provided. The surface acoustic wave resonator includes a piezoelectric material layer, an interdigital transducer and a reflective electrode structure; the piezoelectric material layer includes a first region and two second regions arranged in a first direction; the interdigital transducer is located at a side of the piezoelectric material layer; the reflective electrode structure is arranged in the same layer as the interdigital transducer; the first region is located between two second regions, the interdigital transducer is located in the first region, the reflective electrode structure is located in the second region, and the surface acoustic wave resonator further includes a groove located in the piezoelectric material layer, the groove is located in the second region, and is located at a side of the reflective electrode structure away from the interdigital transducer in the first direction.

In an elastic wave element, an interdigital transducer electrode includes a first layer including a first material having conductivity. The first layer has a thickness greater than 100 . The first layer is superposed on the piezoelectric layer directly or with a metal layer of smaller than or equal to 100 interposed between the first layer and the piezoelectric layer. When a pitch of electrode fingers of the interdigital transducer electrode is p (m) and a value obtained by dividing a thickness of the first layer (m) by 2p.sup.0.101 is a normalized thickness t1, the normalized thickness t1 and an acoustic velocity V1 (m/s) of a bulk longitudinal wave propagating through the first material satisfy an expression below:

[00001]$2.1410^{6}V1-1.16{10}^{-2}<t1<1.17{10}^{-5}V1-1.63{10}^{-2}.$

In a composite filter device, a first acoustic wave resonator includes a functional electrode on a first main surface of a first piezoelectric substrate, and a wiring electrode is on the first main surface and is not connected to a signal potential. A support is on the first main surface and surrounds the first acoustic wave resonator. A second piezoelectric substrate is on the support and includes a third main surface closer to the support than a fourth main surface. A second acoustic wave resonator includes a functional electrode on the third main surface. The second acoustic wave resonator is a parallel-arm resonator higher in resonant frequency than any other parallel-arm resonator or a series-arm resonator lower in resonant frequency than any other series-arm resonator. The second acoustic wave resonator and the wiring electrode overlap each other when viewed in plan.