PURPOSE: To accelerate the data replacing speed without accelerating the transmitting speed, by dividing the process input/output units having high data replacing speeds into minor groups and including these groups into a process input/ output receiver to collect data.

CONSTITUTION: Plural PIO receivers 30W35 belong to a process input/output PIO driver 20 which holds the data to be supplied to a CPU10. Each of these receivers has plural PIO units 40W48. In this case, the PIO units having a high data replacing speed are divided into minor groups as small as possible. Polling is applied to the receivers 30W35 from a driver 20 to give a command for successive and circular transmission of data. Then the receiver received the command selects successively and circularly only the data equivalent to a group of each unit among its belonging PIO units and then delivers only the selected data to a command. In such a way, the PIO unit having high data replacing speeds can be realized.