An acoustic wave element is used for a filter and a duplexer used for a mobile communication apparatus. A surface acoustic wave element, a boundary acoustic wave element or a love wave element is used as such an acoustic wave element. The acoustic wave element includes an IDT (Interdigital Transducer) formed on a piezoelectric substrate. An edge reflection type acoustic wave element that reflects an acoustic wave excited by the IDT by using an end face is disclosed in documents (e.g. Japanese Patent Application Publication Nos. 7-263998, 2000-59175, 2001-339271, 2001-94374, 2002-368576 and 2007-20234).
In the edge reflection type acoustic wave element, a reflector is unnecessary and downsizing of the acoustic wave element is possible, compared with an acoustic wave element that reflects the acoustic wave excited by the IDT by using the reflector. Moreover, by controlling a bulk wave which occurs between the IDT and the reflector, low loss becomes possible.
However, in the edge reflection type acoustic wave element, a width of an electrode finger nearest to each of end faces is set to one half of the widths of other electrode fingers. When a frequency of a signal which excites the acoustic wave becomes high, the widths of the electrode fingers become narrow. Thus, in order to form the narrow electrode fingers, it becomes difficult to manufacture the acoustic wave element cheaply and easily.