PURPOSE: To remove a direct current component regardless of the signal component included in the input in a short time without generating the phase dislocation with an output signal by specifying the amplification factor of an amplifier so that the direct current component can be removed.

CONSTITUTION: The filter is equipped with a low-pass filter 1, a sample/hold circuit 2 to sample-hold an input signal through the low-pass filter at the elapsed time point of a prescribed time (t) from the input starting of an input signal, an amplifier circuit 4 to amplify the sample held signal at an amplification factor A given at A=1/(1-e-ωcxt) by a cut-off frequency ωc of the low-pass filter and the time (t) and a differential circuit 5 to subtract an amplifying signal from an input signal. Thus, the direct current component regardless of the signal component included the input can be removed in a short time while the phase dislocation does not occur.