Filter device and multiplexer

A filter device comprising:

• a piezoelectric substrate and a plurality of acoustic wave resonators on the piezoelectric substrate;
• wherein
• the plurality of acoustic wave resonators includes a plurality of series arm resonators and at least one parallel arm resonator;
• the plurality of series arm resonators includes at least one first series arm resonator and at least one second series arm resonator, the at least one second series arm resonator being different from the at least one first series arm resonator;
• a resonant frequency of the at least one first series arm resonator is higher in frequency than a pass band of the filter device;
• the at least one second series arm resonator has a series connection configuration in which at least two series arm resonators are connected in series to one another;
• and
• when, in the at least two series arm resonators, an electrode finger pitch of the series arm resonator with a largest electrode finger pitch is expressed as P2max, an electrode finger pitch of the series arm resonator with a smallest electrode finger pitch is expressed as P2min, and an electrode finger pitch of the at least one first series arm resonator is expressed as P1, a following relationship is satisfied:
• P2min≤(1+0.01×BWe/2)×P1≤P2max
• where BWe={(a filter device pass band upper limit frequency−a filter device pass band lower limit frequency)×2.3/a pass band center frequency}×100[%].