PURPOSE: To shorten training time required for setting an initial phase by providing a sampler, plural initial phase setting circuits to input sampled signals, and maximum value detection circuit to input the outputs of these circuits.

CONSTITUTION: A signal propagated through a subscriber's line 101, passed through a hybrid transformer 102 and A/D converted by an A/D converter 103 is thinned by a sampler 107. A thinned signal is turned to the signals of four points at equal intervals within a baud rate, namely, of four different phases in the baud rate. Since initial phase setting circuits 108-111 input signals 112 thinned into T/4 by the sampler 107, the phases of signals inputted to the respective circuits 108-111 are shifted just for T/4. Thus, the sampler 107 samples the signals at T/4, successive switching is enabled like switches (a)→(b)→(c)→(d)→(a)... on the initial phase setting side, the signals inputted to the circuits 108 to 111 are turned to the data of a baud rate cycle, and the training time is shortened to 1/4.