A resonant device includes first and second piezoelectric thin film resonators. The first piezoelectric thin film resonator includes a substrate, a first lower electrode formed on the substrate, a first piezoelectric film formed over the first lower electrode, and a first upper electrode formed on the piezoelectric film and opposed to the first lower electrode. The second piezoelectric thin film resonator includes a second lower electrode formed above the first upper electrode, a second piezoelectric film formed over the second lower electrode, and a second upper electrode formed on the piezoelectric film and opposed to the second lower electrode. The first membrane region in which the first lower electrode opposes to the first upper electrode through the first piezoelectric film and a second membrane region in which the second lower electrode opposes to the second upper electrode through the second piezoelectric film are laminated through a second cavity.