PURPOSE: To use in common a data bus and to simplify the constitution by storing the information "0" in an artificial input/output device, and resetting plural buffers in the input/output control device by use of this information.

CONSTITUTION: A microprocessor device MP stores in advance "0", and a parity it "1" at a prescribed position in an artificial input/output device PIO. Subsequently, the device MP gives an instruction to data buffers DB0WDB2 so that data is transferred to an I/O device, and the data is not transferred to a storage device MEM. As a result, the buffers DB0WDB2 read out contents of the device PIO and store automatically its data "0". In this way, reset is executed automatically, and the devices DB0WDB2 do not use a data bus between the device MP and themselves. Accordingly, one data bus is used in common, and constitution of a circuit can be simplified.