In recent years, the development has been underway of filter elements for high-frequency communications characterized in allowing only electronic signals in a certain frequency band to pass therethrough, which characteristic being achieved by the combination of a plurality of resonators using surface acoustic waves (SAWs) by using a piezoelectric material or resonators using thickness vibration waves of a piezoelectric film (FBARs). Because filter components utilizing SAW resonators or FBARs are smaller in outer size than other dielectric and ceramics filters and have steep roll-off properties, they are suitable for components of mobile communication devices such as mobile phones whose components need to be small and have a narrow fractional bandwidth. Duplexers are components to which SAW and FBAR ladder filters are applied. Duplexers have been used in wireless devices that have transmission and reception capabilities and transmit and receive signals of different frequencies. In duplexers, unbalanced transmitting filters, and unbalanced input-balanced output receiving filters having an output impedance of 100Ω are required in recent years, so that the output impedance becomes larger than the input impedance.
Patent Document 1 discloses a multimode SAW filter in which unbalanced to balanced conversion and input to output conversion can be implemented. Patent Document 2 discloses an MEMS resonator in which unbalanced to balanced conversion can be implemented.    Patent Document 1: JP 2008-283425 A    Patent Document 2: JP 2005-094568 A
However, Patent Documents 1 and 2 do not disclose an FBAR in which unbalanced to balanced conversion can be implemented. The inventors found that with the configurations disclosed in Patent Documents 1 and 2, it is difficult to achieve a high Q filter.