PURPOSE: To eliminate crosstalk to a subscriber line and to reduce the power consumption of a ping-pong transmission system by varying the transmission level of a station burst signal according to whether or not the subscriber line is long.

CONSTITUTION: The arrival period of a subscriber burst signal detected by a synchronizing circuit 20 is sent to a delay time detecting means 21 and compared with the transmission period of the station burst signal to finds a transmission delay time. Then a delay time detecting means 21 compares a prescribed transmission delay time corresponding to the length of the constant-length subscriber line with the found transmission delay time and starts a switching means 22 in case of deciding that the found delay time is longer than the prescribed transmission delay time to vary the transmission level of a transmission driver 11 to a transmission level corresponding to the subscriber line length. Thus, the local burst signal with the proper level is sent out to both a short-distance subscriber line and a long-distance subscriber line. Therefore, the crosstalk to the subscriber line is eliminated and the power consumption is reduced.