Some interface signals are selected from among signals of a plurality of different parallel interfaces, then being multiplexed onto a serial connection. A transmitter of a signal transmission system includes an interface-signal selector IFS, and a transfer programmer TP for issuing a control signal to instruct the selection from among the parallel interfaces. The transfer programmer TP implements the multiplexing of the selected interface signals in such a manner that the specification of the parallel interfaces is satisfied. Also, the transfer programmer TP changes, as occasion requires, the control signal to instruct which interfaces to select. This change allows the interface signals to be multiplexed onto the serial connection while dynamically changing the interface signals to be multiplexed.