PURPOSE: To omit a low group pilot signal rejector and a pilot signal transmitter on the terminal side by providing a high group pilot signal detector to a high group signal input part of a bidirectional repeating amplifier.

CONSTITUTION: The high group pilot signal detector 18 extracts only a pilot signal for AGC out of high group signals SH obtained from a center head end, and outputs a detected output proportional to the receiving level to an AGC driving circuit 19 as a signal S18. The circuit 19 sends a driving signal S19 corresponding to the signal S18 to a low group AGC driving circuit 20. The circuit 20 executes the automatic gain control of a low group signal SL obtained from a low group signal amplifier 17 on the basis of the signal S19 and outputs the gain-controlled low group signal SL to an I/O terminal 12 through another low group signal amplifier 21 and a high group/low group distributor 13. Thus, the AGC of the low group signal SL can be attained by always detecting the level of the high group pilot signal, converting the detected level into a low group variable and supplying the variable to the circuit 20.