REPEATER

PROBLEM TO BE SOLVED: To obtain the repeater through which a subordinate device detects an alarm display signal immediately by operating a signal transmission section with an asynchronizing signal whose phase is in matching with a synchronizing clock signal. SOLUTION: When a line is interrupted, a phase comparator 31 compares a phase of a synchronizing clock from a frame synchronization circuit 13 with a phase of an asynchronizing clock from an internal oscillator 19. Then the phase of the asynchronizing clock is delayed with a delay circuit (DLY) 32 by a phase difference detected by the phase comparator 31. Then a selector (SEL) 18 selects an internal oscillator 18 to activate a signal transmission section 14 with its asynchronizing clock whose phase is in matching with the synchronizing clock. Since the phase of the clock at an input terminal of the SEL 18 is matched, a phase of output data from a signal transmission section 14 is not rapidly changed and no out of frame synchronism is detected by a repeater and a multiplex terminator at a subordinate stage and an alarm display signal is immediately detected.