An elastic wave filter device comprising: a serial arm connecting an input terminal to an output terminal, a parallel arm connecting the serial arm to a ground potential, and a plurality of elastic wave resonators (S1-1 to S3-3, P1-P3) disposed in the serial and parallel arms, wherein each of the elastic wave resonators (S1-1 to S3-3, P1-P3) includes a piezoelectric substrate and an IDT electrode formed on the piezoelectric substrate, wherein the IDT electrode includes a first busbar, a second busbar spaced from the first busbar, a plurality of first electrode fingers, each base end of which being electrically connected to the first busbar, that extend towards the second busbar side, and a plurality of second electrode fingers, each base end of which being electrically connected to the second busbar, that extend towards the first busbar side and are interleaved with the plurality of first electrode fingers, wherein the IDT electrode further includes a central area in the center of the IDT electrode in a direction in which the first and second electrode fingers (23,24) of the IDT electrode extend and overlap with each other, a low acoustic velocity area at an outer side portion of the central area in a direction in which the electrode fingers extend, the low acoustic velocity area having an acoustic velocity (V 2) that is relatively low in comparison with the acoustic velocity (V 1) of the central area, and a high acoustic velocity area at an outer side portion in a direction in which the low acoustic velocity area extends on the side opposite to the central area, the high acoustic velocity area having an acoustic velocity (V 3) that is higher than the acoustic velocity (V 1) in the central area, wherein the width (W 1) of the low acoustic velocity area in the width direction of at least one elastic wave resonator differs from the width of the low acoustic velocity area of the other elastic wave resonators, the width direction being a direction orthogonal to the elastic wave propagation direction, and wherein the first and second busbars respectively include an inner side busbar section, a central busbar section, and an outer side busbar section, wherein the inner side busbar section has a belt-like shape, wherein a plurality of cavities is provided in the central busbar section, wherein the central busbar section is the high acoustic velocity area, wherein the base ends of the first and second electrode fingers (23,24) include convex portions, wherein wide width portions, having projections in the width direction of the fingers, are provided at the leading end side of the first and second electrode fingers (23,24), and wherein the inner side busbar section, the convex portions, and the wide width portions form the low acoustic velocity area. a serial arm connecting an input terminal to an output terminal, a parallel arm connecting the serial arm to a ground potential, and a plurality of elastic wave resonators (S1-1 to S3-3, P1-P3) disposed in the serial and parallel arms, wherein each of the elastic wave resonators (S1-1 to S3-3, P1-P3) includes a piezoelectric substrate and an IDT electrode formed on the piezoelectric substrate, wherein the IDT electrode includes a first busbar, a second busbar spaced from the first busbar, a plurality of first electrode fingers, each base end of which being electrically connected to the first busbar, that extend towards the second busbar side, and a plurality of second electrode fingers, each base end of which being electrically connected to the second busbar, that extend towards the first busbar side and are interleaved with the plurality of first electrode fingers, wherein the IDT electrode further includes a central area in the center of the IDT electrode in a direction in which the first and second electrode fingers (23,24) of the IDT electrode extend and overlap with each other, a low acoustic velocity area at an outer side portion of the central area in a direction in which the electrode fingers extend, the low acoustic velocity area having an acoustic velocity (V 2) that is relatively low in comparison with the acoustic velocity (V 1) of the central area, and a high acoustic velocity area at an outer side portion in a direction in which the low acoustic velocity area extends on the side opposite to the central area, the high acoustic velocity area having an acoustic velocity (V 3) that is higher than the acoustic velocity (V 1) in the central area, wherein the width (W 1) of the low acoustic velocity area in the width direction of at least one elastic wave resonator differs from the width of the low acoustic velocity area of the other elastic wave resonators, the width direction being a direction orthogonal to the elastic wave propagation direction, and wherein the first and second busbars respectively include an inner side busbar section, a central busbar section, and an outer side busbar section, wherein the inner side busbar section has a belt-like shape, wherein a plurality of cavities is provided in the central busbar section, wherein the central busbar section is the high acoustic velocity area, wherein the base ends of the first and second electrode fingers (23,24) include convex portions, wherein wide width portions, having projections in the width direction of the fingers, are provided at the leading end side of the first and second electrode fingers (23,24), and wherein the inner side busbar section, the convex portions, and the wide width portions form the low acoustic velocity area.