PURPOSE: To attain the efficient line design at a low cost by controlling a standby transmission equipment so as to output a same output as that of an active transmission equipment when the active transmission equipment is faulty and controlling the standby transmission equipment so as to output a rated output higher than the output of the active transmission equipment in the normal state when a reception input of an opposite receiver is lowered abnormally.

CONSTITUTION: A controller 3 being a CONT at a sender side 100 acts like controlling the changeover of a #1 transmission equipment (standby) with a device fault alarm from a #2 transmission equipment (active) and like controlling the output of the #1, #2 transmission equipments with a reception alarm representing an abnormally low reception input due to occurrence of fading coming from an opposite reception station 200 in common. The standby ≥1 transmission equipment of the sender side 100 consists of a modulator MOD1 and a transmitter TX1, the active #2 transmission equipment comprises a modulator MOD2 and a transmitter TX2, and the system whose transmission output is decreased in the normal state is selected as the active system 2 and the system increasing the transmission output in the occurrence of fading is selected as the standby system #1. Since the transmission output of the standby system #1 is increased in the occurrence of fading, a variable attenuator 21 whose attenuation is decreased by a control voltage V being an output of the controller 3 being the CONT is inserted to an intermediate frequency stage between the modulator MOD1 and the transmitter TX1 of the standby #1 transmission equipment.