PURPOSE: To improve the transmission efficiency of data transmission by shortening the adjustment time of an automatic equalizer before data reception.

CONSTITUTION: In a MODEM transmission part 9 of the other station, turning-on of a power source part 13 is detected by a counter 15. A control part 14 adds an address signal and a training signal to this detection state discrimination signal to transmit it to a local MODEM reception part 1 of one station. In this reception part 1, each signal is detected by a detecting part 4, and a control part 5 discriminates first reception by the state discrimination signal and adjusts an automatic equalizer 6 in the same procedures as conventional. The address signal and equalizer set information are stored in a storage part 7. When data is received again, the contrl part 5 in the MODEM reception part 1 of one station discriminates second reception by the state discrimination signal and reads out equalizer set information stored in the storage part 7 by the address signal to perform automatic adjustment. The adjustment time at this time is considerably shorter than the first adjustment.