An acoustic wave device includes a piezoelectric substrate made of LiNbO.sub.3, and a dielectric film provided on the piezoelectric substrate to cover first and second IDT electrodes on the piezoelectric substrate. The first and second IDT electrodes include main electrode layers. When wave lengths determined by electrode finger pitches of the first and second IDT electrodes are .sub.1 and .sub.2, respectively, the average value thereof is .sub.0, .sub.1/.sub.0=1+X, and .sub.2/.sub.0=1X, a relationship of 0.05X0.65 is satisfied. The wavelength .sub.1 is the longest, and the wavelength .sub.2 is the shortest. In Euler angles (, , ) of the piezoelectric substrate, is 05, is 010, and satisfies Expression 1, wherein a relationship of B.sub.1<Tr0.10.sub.0 and B.sub.2<Tr0.10.sub.0 are satisfied.

A filter (10) has a first passband and a second passband on a higher frequency side than the first passband and includes a series arm circuit (11) and a parallel arm circuit (12), wherein the parallel arm circuit (12) includes a parallel arm resonator (p1) connected between a node (x1) and ground and having a resonant frequency frp located between a first passband and a second passband, an inductor (L1) connected between the node (x1) and the ground, and an inductor (L2) connected between the node (x1) and the ground and connected in series to the parallel arm resonator (p1), and a circuit in which the parallel arm resonator (p1) and the inductor (L2) are connected in series is connected in parallel to the inductor (L1).

A filter (10) has a first passband and a second passband on a higher frequency side than the first passband and includes a series arm circuit (11) and a parallel arm circuit (12), wherein the parallel arm circuit (12) includes a parallel arm resonator (p1) connected between a node (x1) and ground and having a resonant frequency frp located between a first passband and a second passband, an inductor (L1) connected between the node (x1) and the ground, and an inductor (L2) connected between the node (x1) and the ground and connected in series to the parallel arm resonator (p1), and a circuit in which the parallel arm resonator (p1) and the inductor (L2) are connected in series is connected in parallel to the inductor (L1).

A branching 1 filter has an antenna terminal 3 which receives signal waves and disturbance waves, a transmission filter 11 which is connected to the antenna terminal 3, a reception filter 13 which is connected to the antenna terminal 3 and receives a portion of the signal waves and has, as a passband, a frequency range higher than a passband of the transmission filter 11, and a disturbance wave resonator which is connected to the antenna terminal 3 and to the ground and positioned closer to the antenna terminal 3 side than the transmission filter 11 and the reception filter 13. The disturbance wave resonator 15 is connected to antenna terminal 3 at a position closer to the antenna terminal 3 side than the transmission filter 11 and the reception filter 13. A resonance frequency of the disturbance wave resonator 15 is within a frequency range smaller than the passband of the transmission filter and includes a frequency range of the disturbance waves.

A branching 1 filter has an antenna terminal 3 which receives signal waves and disturbance waves, a transmission filter 11 which is connected to the antenna terminal 3, a reception filter 13 which is connected to the antenna terminal 3 and receives a portion of the signal waves and has, as a passband, a frequency range higher than a passband of the transmission filter 11, and a disturbance wave resonator which is connected to the antenna terminal 3 and to the ground and positioned closer to the antenna terminal 3 side than the transmission filter 11 and the reception filter 13. The disturbance wave resonator 15 is connected to antenna terminal 3 at a position closer to the antenna terminal 3 side than the transmission filter 11 and the reception filter 13. A resonance frequency of the disturbance wave resonator 15 is within a frequency range smaller than the passband of the transmission filter and includes a frequency range of the disturbance waves.

An acoustic wave device includes a piezoelectric substrate made of LiNbO.sub.3, and a dielectric film provided on the piezoelectric substrate to cover first and second IDT electrodes on the piezoelectric substrate. The first and second IDT electrodes include main electrode layers. When wave lengths determined by electrode finger pitches of the first and second IDT electrodes are .sub.1 and .sub.2, respectively, the average value thereof is .sub.0, .sub.1/.sub.0=1+X, and .sub.2/.sub.0=1X, a relationship of 0.05X0.65 is satisfied. The wavelength .sub.1 is the longest, and the wavelength .sub.2 is the shortest. In Euler angles (, , ) of the piezoelectric substrate, is 05, is 010, and satisfies Expression 1, wherein a relationship of B.sub.1<Tr0.10.sub.0 and B.sub.2<Tr0.10.sub.0 are satisfied.

An acoustic wave device includes a piezoelectric substrate made of LiNbO.sub.3, and a dielectric film provided on the piezoelectric substrate to cover first and second IDT electrodes on the piezoelectric substrate. The first and second IDT electrodes include main electrode layers. When wave lengths determined by electrode finger pitches of the first and second IDT electrodes are .sub.1 and .sub.2, respectively, the average value thereof is .sub.0, .sub.1/.sub.0=1+X, and .sub.2/.sub.0=1X, a relationship of 0.05X0.65 is satisfied. The wavelength .sub.1 is the longest, and the wavelength .sub.2 is the shortest. In Euler angles (, , ) of the piezoelectric substrate, is 05, is 010, and satisfies Expression 1, wherein a relationship of B.sub.1<Tr0.10.sub.0 and B.sub.2<Tr0.10.sub.0 are satisfied.