PURPOSE: To obtain a stable amplifying circuit having broad frquency selectivity, by alternately locating the elastic surface wave filter different from the center frequencies and the amplifier section.

CONSTITUTION: The elastic surface wave filters 6∼8 have the pass band characteristics 16∼18 different from the center frequency. The characteristics of each elastic surface wave filter is for conventional narrow band. As the amplifying circuit, the filters 6∼8 and the amplifiers 3a∼3c are alternately located, and broad characteristic circuit is used for the amplifying circuit. Since the center frequency of the elastic surface wave filter is shifted, self-oscillation is hardly taken place and broad band characteristics can be obtained for overall characteristics.