PURPOSE: To send a sufficient signal voltage to a reception station by providing a reactor compensating the signal attenuation due to the ground capacitance of a line in parallel with each transmission and reception station so as to cancel the signal leakage effect.

CONSTITUTION: A signal current is transmitted from a master station 3 (or slave station 4) and received by the slave station 4 (or master station 3) via a distribution line 2, and returns to the original sending end through ground. In such a case, the effect of leakage of a signal current though a ground stray capacity 5 of the line is cancelled by adjusting the variable reactor 6a of the master station or the variable reactor 6b of the slave station so as to send the sufficient level of signal voltage to the reception station.