PURPOSE: To make unnecessary the synchronism of clock, by detecting the phase difference of the transmission and reception baud rate clock and shifting the tap coefficient of the transversal filter by one stage when the phase difference is in excess of +2π and -2π.

CONSTITUTION: The output signal of the transversal filter 1 inputting the transmission symbol series is subtracted from the reception signal with the subtractor 2, and the output is sampled at the sampler 3 in the reception baud rate clock. Next, the tap coefficient of the filter 1 is corrected with the tap coefficient circuit 5 from the differential signal of the input and output signal of the discriminator 4. Further, the phase difference between the transmission baud rate clock R1 and the reception baud rate clock R2 is detected at the phase comparator 6, and when the phase difference is in excess of +2π, -2π, based on the polarity of the respective phase difference, the tap coefficient of the filter 1 is shifted right or left by one stage with the tap coefficient circuit. Accordingly, the operation is made with determined baud rate and no establishment of the synchronism of the transmission baud rate clock between MODEM's opposed is required.