A base band circuit of a receiver and a low cut-off frequency control means can quickly converge transition state due to gain fluctuation with setting a low cut-off frequency of a high-pass filter as low as possible. The base band circuit of a receiver has a variable amplifier variably amplifying a base band signal depending upon a gain control signal, a high-pass filter provided in a path of the base band signal, and a controller detecting variation magnitude of the gain control signal and controlling variation of a low cut-off frequency of the high-pass filter means depending upon the detected variation magnitude.