PURPOSE: To decrease the number of transmission lines after securing the using and spare systems and to reduce the cost of facilities by using two types of intermediate frequency bands to synthesize the using and spare intermediate frequencies of a TV signal for transmission.

CONSTITUTION: The inputs 1 and 2 of the 1st and 2nd TV signals are distributed to the using and spare systems by signal distributors 3 and 4. The frequency converters 5 and 8' convert frequencies into the 1st intermediate frequency band; while the frequency converters 6' and 7 convert frequencies into the 2nd intermediate frequency band respectively. These converters are connected to filter demultiplexers 13 and 14 which separate the 1st and 2nd intermediate frequency bands via filter synthesizer 11 and 12 which synthesize the 1st and 2nd intermediate frequency bands. Furthermore the frequency converters 15 and 18' which convert the intermediate frequencies corresponding to the 1st and 2nd input signals which are converted into the 1st intermediate frequency band and transmitted into a transmission frequency band are added together with the frequency converters 16' and 17 having the similar constitutions as converters 15' and 18 and convert the frequencies into the 2nd intermediate frequency band for transmission. Thus two types of intermediate frequencies are provided to perform the multiplex transmission with synthesization and distribution. In addition, both using and spare systems are connected alternately and therefore the 1st and 2nd input signals can be transmitted despite a defective transmission line.