A frequency characteristics-controlling device which comprises an operational amplifier provided with two input terminals mutually bearing an inversion-noninversion relationship with respect to an output signal; a bridged-T circuit consisting of resistors and capacitors, the input terminal of said bridged-T circuit being connected to the inversion input terminal of said amplifier and the output terminal of said bridged-T circuit being connected to the output terminal of said amplifier; a first gain-controlling circuit connected between the common terminal of the bridged-T circuit and the noninversion input terminal of the amplifier; and a second gain-controlling circuit connected between the common terminal of the bridged-T circuit and the output terminal of the amplifier, whereby the frequency characteristics of an input signal supplied to the noninversion input terminal of the operational amplifier are controlled by the first and second gain-controlling circuits.