PURPOSE: To improve the filter insertion loss and the frequency response characteristic due to impedance mismatching between an externally mounted input/output circuit and a surface acoustic filter by forming a thin film coil on a substrate where a piezoelectric vibrator is formed.

CONSTITUTION: A multistrip coupler 13 formed as a pattern is provided at the center of the substrate between reed screen electrodes 11 and 12 on which a minute electrode pattern is formed. The multistrip coupler 13 makes the strength of a propagating plane of an ultrasonic wave vibrating frequency energy uniform between reed screen electrodes 11 and 12 so as to block the spurious radiation at conversion. Moreover, the substrate plane is provided with a coil 14 formed by the thin film vapor-deposition method coupled directly to an input terminal 6 of the reed screen electrode pattern 11 and a coil 15 formed by the thin film vapor-deposition method coupled directly to an output terminal 7 of the reed screen electrode pattern 12.