Disclosed is a variable gain circuit including a gain change region in which the gain is changed substantially exponentially as a function of a control voltage. The gain is changed in the gain change region substantially exponentially based on a function {(1+x)2+K}/{1−x}2+K}, where x is a control voltage and K is a parameter of K≦1. The parameter K of the function is about equal to 0.21. The denominator and the numerator of the function are proportionate to driving currents of OTAs (operational transconductance amplifiers). Or, the denominator and the numerator of the above function are constituted by output currents of a MOS differential pair and a quadritail cell that includes four transistors driven by a common tail current. Outputs of two of the transistors, receiving a differential input voltage, are connected in common and outputs of the other two of the transistors, receiving the common mode voltage of the differential input voltage, are connected in common.