PURPOSE: To always transmit data even when much noise or distortion exist on a transmission path by setting a data speed according to the size of the equalizing residual quantity (error signal) of an automatic equalizer at the time of training completion.

CONSTITUTION: When a training signal is sent from a modem 15, the training signal through the transmission path is received by a modem 16, tap updating is carried out by an automatic equalizer 2, and the training is carried out. A rate sequence is generated in a rate sequence generating circuit 10 so that a rate sequence may be set at the signal at the higher data speed, when the output signal in a averaging circuit 6 is smaller than a threshold value TH 8 at the time of the training completion, and the rate sequence may be set at the signal at the lower data speed in a contrary case. the generated rate sequence is constituted as the training signal by a training signal generating circuit 11, and sent to the transmission path through a modulating part 12. The sent training signal is received by the modem 15, and in the same way, the training of an automatic equalizer 2 is carried out.