PURPOSE: To eliminate the need for an input/output (I/O) command storage part by providing the peripheral controller with a display means for displaying whether an I/O start from a master device is applied from a master device to the slave device of either one of control part of plural control parts in a single port part connected to the master device or not.

CONSTITUTION: The peripheral controller is provided with the control parts 12, 13 arranged between the single port part 11 connected to the master device and plural peripheral equipments a-x and respectively constituted of microprocessors, an access competition resolving part 14 and the display means 21 arranged in the port part 11 to display whether an I/O start from the master device is included in the slave device of either one of the control part or not. Consequently, the existence of an I/O command to a self device can be easily decided and an I/O command storage part can be omitted.