In a case where signals branched from a single reference signal source are transmitted via a plurality of cables, a phase synchronization circuit can be used to stabilize a phase of a signal to be outputted from each cable. However, the phases of signal to be outputted from each cable is affected by combination of a length of each cable and an amount of delay caused by feedback control, so that phases of synchronization signals to be outputted from a plurality of transmission paths are not always the same as each other. In the present invention, since a frequency multiplier that multiplies a frequency of a signal outputted from each transmission path by an even number is provided for a phase synchronization circuit, the phases of the synchronization signals to be outputted from the transmission paths are aligned even when signals are branched from one reference signal.