In order to enhance the general-purposeness of a time domain multiplexer for digital channel-signals of unequal bit rates, the time domain multiplexer is constructed of a plurality of channel units (7) which provide information signals and bit rate signals of input channel signals, a plurality of logic circuits (37 ... 45) which multiplex the information signals from the channel units (7), and a control circuit (46 ... 50) which selects and combines the logic circuits (37 ... 45) in accordance with the bit rate signal so as to construct a multiplexer conforming with the bit rate.