PURPOSE: To suppress increases in crosstalk by providing a passive band stop filter circuit and a positive feedback circuit adjusting continuously the positive feedback amount to the said passive band stop filter circuit.

CONSTITUTION: The passive band stop filter 11 consists of a twin T circuit and a bridge T circuit, and the variable positive feedback circuit 13 consists of a fixed gain amplifier circuit 13a and a variable attenuator 13b. The positive feedback amount to the passive band stop filter circuit 11 is adjusted by adjusting the variable attenuator 13b. Thus, increases in crosstalk caused by variance in characteristic of each device or filter, aged change or temperature fluctuation are suppressed simply.