PURPOSE: To improve the reliability of a repeating device by having the synchronism between local oscillation signals of using and spare systems on the basis of the output a prescribed reference oscillator and therefore synthesizing and delivering the output signals of each transmission part to prevent a short break due to the switching of a relay.

CONSTITUTION: A high frequency reception input signal f1 is supplied to FM repeaters 2 and 3 of the currently using and spare systems respectively from a high frequency distributor 1. Then high frequency transmission output signals f2 and f3 are delivered via a reception part 11 and a transmission part 12. The reference signal of a reference signal generator 17 is supplied to the parts 11 of repeaters 2 and 3, reception local oscillators 13' and 15' of the part 12 and transmission local oscillators 14' and 16' respectively. The synchronism is obtained by the output of the generator 17 among the oscillation signals of those oscillators 13', 15', 14' and 16' respectively. Then an output signal f2 given from the repeater 2 is applied to a synthesizer 5 via a phase shifter 6 and synthesized with the output signal f3 of the repeater 3. Then f2=f3 is satisfied to prevent a short break due to the switching of a relay.