A transmission system, having a transmitting device and a receiving device, configured to divide a time division multiplexing, TDM, signal including a series of data streams into a plurality of unit data and transmitting the plurality of unit data, wherein the transmitting device includes: a synchronization unit configured to output a clock signal synchronized with the receiving device by communicating synchronization unit data with the receiving device; a set of frequency change units (12-1, 12-2) and a set of conversion units (13-1, 13-2) for each of a plurality of TDM signals with different frequencies and each frequency change unit (12-1, 12-2) configured to change a frequency of a TDM signal on the basis of a clock signal output from the synchronization unit of its own device and each conversion unit (13-1, 13-2) configured to converts the TDM signal with the changed frequency into a plurality of unit data and transmitting the plurality of unit data to the receiving device. and the receiving device includes: a synchronization unit configured to output a clock signal synchronized with the transmitting device by communicating synchronization unit data with the transmitting device; a set of decoding units (22-1, 22-2) and a set of frequency restoration units (23-1, 23-2) in the same number as that of the set of the frequency change units (12-1, 12-2) and the set of conversion units (13-1, 13-2) of the transmitting device, and each decoding unit (23-1, 23-2) configured to receive the plurality of unit data from the transmitting device and to restore a TDM signal with the changed frequency and each frequency restoration unit (23-1, 23-2) configured to restore the TDM signal by returning a frequency of the TDM signal with the changed frequency to an original frequency on the basis of the clock signal output from the synchronization unit of its own device. a synchronization unit configured to output a clock signal synchronized with the receiving device by communicating synchronization unit data with the receiving device; a set of frequency change units (12-1, 12-2) and a set of conversion units (13-1, 13-2) for each of a plurality of TDM signals with different frequencies and each frequency change unit (12-1, 12-2) configured to change a frequency of a TDM signal on the basis of a clock signal output from the synchronization unit of its own device and each conversion unit (13-1, 13-2) configured to converts the TDM signal with the changed frequency into a plurality of unit data and transmitting the plurality of unit data to the receiving device. and the receiving device includes: a synchronization unit configured to output a clock signal synchronized with the transmitting device by communicating synchronization unit data with the transmitting device; a set of decoding units (22-1, 22-2) and a set of frequency restoration units (23-1, 23-2) in the same number as that of the set of the frequency change units (12-1, 12-2) and the set of conversion units (13-1, 13-2) of the transmitting device, and each decoding unit (23-1, 23-2) configured to receive the plurality of unit data from the transmitting device and to restore a TDM signal with the changed frequency and each frequency restoration unit (23-1, 23-2) configured to restore the TDM signal by returning a frequency of the TDM signal with the changed frequency to an original frequency on the basis of the clock signal output from the synchronization unit of its own device. a synchronization unit configured to output a clock signal synchronized with the transmitting device by communicating synchronization unit data with the transmitting device; a set of decoding units (22-1, 22-2) and a set of frequency restoration units (23-1, 23-2) in the same number as that of the set of the frequency change units (12-1, 12-2) and the set of conversion units (13-1, 13-2) of the transmitting device, and each decoding unit (23-1, 23-2) configured to receive the plurality of unit data from the transmitting device and to restore a TDM signal with the changed frequency and each frequency restoration unit (23-1, 23-2) configured to restore the TDM signal by returning a frequency of the TDM signal with the changed frequency to an original frequency on the basis of the clock signal output from the synchronization unit of its own device.