PURPOSE: To contrive to reduce power consumption of the entire system without losing the reliability and to improve the economy by preparing a standby transmitter having a transmission output level smaller than that of an active transmitter.

CONSTITUTION: In case of one-to-one constitution where one active transmitter and one standby transmitter are provided, a signal sent to an input terminal 1 is branched into two by a signal distributer and inputted respectively to the active transmitter 4 with a prescribed sending output level and to the standby transmitter 3 in the operating state having a smaller transmission output level than that of the active transmitter 4. A switch 5 selects a normal transmission output of the transmitters depending on the transmission state of the active transmitter 4 or the standby transmitter 3 and give the output to an output terminal 6. When both the transmitters are operated normally, the transmission output of the active transmitter 4 is sent to the output terminal 6. In case of the constitution that where N sets of active transmitters and one set of standby transmitter are provided as N to 1 constitution, the active/standby equipments are switched by using one standby transmitter 3 having a smaller transmission output level than that of the active transmitters 4a∼4n with respect to the N-set of the active transmitters 4a∼4n.