To provide a variable gain circuit capable of securing a band during sampling and its application device.

The variable gain circuit comprises: a differential input amplifier 1; switches 21 and 22 for sampling connected between respective signal input terminals and the respective input terminals of the amplifier; feedback capacitors 13 and 14 whose one end is connected to the respective input terminals of the amplifier; switches 17 and 18 for arithmetic operations connected between the other end of the respective feedback capacitors and the respective output terminals of the amplifier; a variable input capacitor circuit 32 composed of first and second input capacitor groups 11 and 12 configured by serially connecting the plurality of capacitors whose one end is connected to the respective input terminals of the amplifier and an input switch group 23 configured by providing for each capacitor an input switch whose one end is connected to the other end side of one capacitor in the first input capacitor group and other end is connected to the other end side of one corresponding capacitor in the second input capacitor group; switches 15 and 16 for setting connected between the respective output terminals of the amplifier and a reference voltage source; and a switch control circuit 39 for controlling the operations of the respective switches.