A tuning amplifier 1 is provided with an oscillation circuit 10 incorporating an amplifier circuit 11 and a feedback circuit 12, an input circuit 14 which inputs signals to the oscillation circuit 10, and an automatic gain control (AGC) circuit 16 which controls the output amplitude of the oscillation circuit 10. When signals are inputted to the oscillation circuit 10 through the input circuit 14, such tuning that only signals having frequencies near the oscillation frequency of the oscillation circuit 10 are allowed to pass through is possible.