PURPOSE: To make it possible that gain changes logarithmic-linearly for the change of a feedback quantity by providing mixer circuits in the output and the input of a gain control circuit, which has an operational amplifier and changes the feedback quantity to control gain, to constitute a variable gain amplifier circuit.

CONSTITUTION: Gain control circuit 1 which is constituted by an operational amplifier and has feedback quantity x generates output xX for the input of state variable X. This output xX is mixed with input signal ei by first mixer circuit 2 and is mixed with the state variable by second mixer circuit 3 to obtain output voltage eo=X+xX. Eo/ei=(1+x)/(1-x) is true because of variable X=ei+xX. When logarithms of gain G=eo/ei are taken and are subjected to progression expansion to take up to the first term, lnG=2x is true, so that gain can be changed logarithmic-linearly for the linear change of the feedback quantity. If a phase switching circuit is provided in the input of circuit 1, the logarithmic-linear attenuation characteristic can be obtained.