PURPOSE: To eliminate baseline wandering while removing zero crossing jitters by restoring the low frequency of the digital signals which are equalized so as to have a flat frequency response.

CONSTITUTION: A clamp circuit 20 clamps a signal A on a line 15 to maximum and minimum peak levels. A signal B, which is clamped, on a line 21 is supplied to a hard limiter 22 and is limited to upper and lower threshold levels. A signal C, which is hard limited, on a line 23 is supplied to a low pass filter 24 and an integrated signal D is obtained. The waveform D is shown by the expanded time scale relative to the waveform A and is used as a correction signal to eliminate the baseline wandering of the equlized signal. An adding circuit 54 couples the signal D on a line 25 to the signal A on the line 15 and supplies an added signal E on a line 27 to a zero crossing detector/decoder 18. Thus, the zero crossing jitter caused by baseline wander is not received.