To provide a switched capacitor filter reducing noise by a simple structure, and also to provide a method of controlling the same.

In this invention, the inverting input of an operational amplifier AMP is connected to one end of an integral capacitor C0 and the output thereof is connected to the other end of the integral capacitor C0. The connection state of this switched capacitor moves in an order of the first to the third. In the first connection state, a first terminal and a second terminal are connected to an input signal and a fixed voltage, respectively. In the second connection state, the first terminal and the second terminal are connected to the fixed voltage and the invertin input of the operational amplifier AMP, respectively. In the third connection state, the first terminal and the second terminal are connected to the output of the operational amplifier AMP and the inverting input of the operational amplifier AMP, respectively. The number of switched capacitors in the second connection state is always the same when one or more of each of the switched capacitors in the second and third connection states exist(s), and the number of the switched capacitors in the third state is always the same as well.