A multiplexing transmission system for adding a management overhead to a client signal, and transparently accommodating or multiplexing the client signal to transmit it is provided. The multiplexing transmission system: accommodates a plurality of client signals of different bit rates including a client signal of a bit rate that is not an integral multiple or an integral submultiple of a bit rate of other client signal, and performs rate adjustment for a part or the whole of the plurality of client signals such that the bit rate of each client signal becomes an integral multiple or integral submultiple of the bit rate of other client signal.