PURPOSE: To suppress the ripples within a pass band to be smale and also to evade the deterioration of NF by providing a surface acoustic wave(SAW) filter and a base-grounded transistor amplifier which amplifies the output signal of the SAW filter.

CONSTITUTION: The output of an SAW filter 2 is inputted to the emitter of a base-grounded transistor TR 8, and the output of the TR 8 is supplied to the base of one of both TRs of a differential amplifier 10. As the base of the other TR of the amplifier 10 is grounded in terms of high frequency, the output signals of the TR 8 are inputted in an unbalanced way. Meanwhile the output of the amplifier 10 is taken out in a balanced way and supplied to a circuit of the next stage. The input impedance of the TR 8 is set at about 50Ω that is equal to 1/4 of about 200Ω of the output impedance of the filter 2. Then the impedance Rs of a signal source is set at 150Ω that is equal to 1/2 of about 300Ω of input impedance of the filter 2 respectively.