1. A low-pass filter comprising: first filtering means that accepts, as an input, an input signal to said low-pass filter and outputs a first voltage; a circuit element included in said first filtering means for allowing a first current to flow in accordance with said first voltage; current generating means for generating a second current at a given rate to said first current; second filtering means that accepts, as an input, said second current and outputs a second voltage; and adding means for adding said first voltage and said second voltage and outputting an output signal of said low-pass filter.