PURPOSE: To stabilize the frequency of a reference signal and to attain broadcast relay with high reliability, by using three reference signals of the reference based on a video carrier, the reference signal based on a chrominance subcarrier and the 3rd reference signal selectively.

CONSTITUTION: A reference signal generating section 8 generates a reference signal (10MHz) from the chrominance subcarrier, a generator 9 generates a reference signal (10MHz) from a video signal and the 3rd oscillator 10 such as a rubidium oscillator generates a reference signal (10MHz). Phase comparators 11∼13 are connected between the two among the three reference signals respectively to form a beat signal. Further, discriminators 14∼16 discriminate whether the beat number exceeds a required number. A control circuit 17 decides which reference signal is to be used based on the result of the discriminator 14 to switch a changeover switch 18. Thus, the reference signal with high accuracy without any shift is inputted to a signal processing section 19.