PURPOSE: To adjust the transmission phase of a slave transmitter without provision of a non-signal region by providing a means to demultiplex a signal incoming from an outgoing transmission line and supplying the signal to a timing measurement means to a master transmitter.

CONSTITUTION: A phase adjustment channel transmission circuit 306 and a directional coupler 307 being means to send a signal requesting timing adjustment to an outgoing transmission line 21 in the opposite direction are provided respectively to each of slave transmitters 30-1 30-n. Then a master transmitter 10 is provided with a directional coupler 103 and a phase adjustment channel reception circuit 104 as means to demultiplex a signal coming from the outgoing transmission line 21 and to supply the signal to a phase adjustment measurement circuit 105. Then the slave transmitters 30-1-30-n detect a phase adjustment request signal coming up reversely through the outgoing transmission line 21 to measure the propagation delay time and the slave transmitters 30-1-30-n adjust the transmission phase of an incoming signal based on the result of measurement. Thus, the transmission efficiency is enhanced.