PURPOSE: To allow the system to cope with instantaneous changeover by fixing the priority of input signals GL.VBS IN and GL.SC IN and selecting automatically either of the signals to use easily a synchronizing signal generator.

CONSTITUTION: A synchronizing signal generator in synchronization coupling with a composite video synchronizing signal (GL.VBS) or a sub carrier signal (SC) being an output of a rubidium oscillator has an input sensing function of the GL.VBS signal and the SC signal, the generator is automatically synchronized-coupled with the GL.VBS when the GL.VBS signal and the SC signal are simultaneously received and the generator is automatically synchronized-coupled with the received signal when only one of the GL.VBS signal and the SC signal is received and the generator outputs a stable synchronizing signal oscillated in itself when both of the GL.VBS signal and the SC signal are received.