PURPOSE: To expand the in-use range of the frequency of a search signal while making possible the fault-point search of a long-distance coaxial transmitting trunk line by biasing a diode, connected between electric power terminals of each repeater, providing low impedance.

CONSTITUTION: To make a search for a fault point, change-over switches 14 and 15 are placed at sides B. At this time, when a Zener voltage across Zener diode 20-2 is set lower than that across Zener diode 20-1, a current from DC power source 16 flows by way of diode 21-2, Zener diode 20-2 and diodes 8 of repeaters 3-2 and 3-1 and diodes 8 operate like switches turn ON. Then when a fault-poing search signal is sent out of pulse generator 11, it reaches fault point 10 by way of power-separating filters 5 and 6 and diodes 8 of repeaters 3-1 and 3-2 and its reflected wave is displayed on oscilloscope 12 by way of the opposite path.