The antenna sharing device has a first elastic-wave filter for passing signals of a first frequency passband and a second elastic-wave filter for passing signals of a second frequency passband higher than the first frequency passband. The first elastic-wave filter is a ladder-type filter including a first series resonator and a second series resonator having an antiresonant frequency point higher than that of the first series resonator. The first series resonator has a first IDT electrode and a first dielectric film covering the electrode. The second series resonator has a second IDT electrode and a second dielectric film covering the electrode. The first and the second dielectric films have a first projection and a second projection, respectively, so as to be formed above the electrode fingers of each IDT electrode. The cross-sectional area of the first projection of the first series resonator is larger than that of the second projection of the second series resonator in the excitation direction of the elastic wave. The structure satisfies both of steepness in a crossband and low loss in a passband.