A filter device includes an acoustic wave resonator including a piezoelectric layer with first and second main surfaces, an IDT electrode on the first main surface and including electrode fingers, a first dielectric film on the first main surface, and a second dielectric film on the second main surface. The first and second dielectric films overlap an overlapping region. A fractional bandwidth is about 8.5% or higher, the fractional bandwidth being ((FH−FL)/FC)×100[%], where FH is a highest frequency of the passband, FL is a lowest frequency of the passband, and FC is a center frequency of the passband. 0.322<(Td_f/Tp)+(Td_b/Tp)<0.786 and |(Td_f/Tp)−(Td_b/Tp)|<0.196, where Tp is a thickness of the piezoelectric layer at the overlapping region, Td_f is a thickness of the first dielectric film overlapping the overlapping region, and Td_b is a thickness of the second dielectric film overlapping the overlapping region.