PURPOSE: To transmit only input information which need be sent as the information varies when more than one kind of information is transmitted through a communication circuit in the form of a signal serial with time.

CONSTITUTION: Command signals S1∼Sn are transmitted to only an input circuit where when the storage contents of the input circuit vary, this varies data need be sent to a reception side as early as possible, only when a parallel-series converting circuit 11 is in a signal input permit state. The input circuit inputting the command signal outputs as address signal, specifying the address of the input circuit, onto an address bus A, and its data signal onto a data bus D. The parallel-series converting circuit 11 inputs the signals from the address bus A and data bus D in bit-parallel form to send bit-series signals.