PURPOSE: To lower the cost for the entirety of a system and to improve the reliability due to the decrease in IOC (input and output control device) by commonly using the IOC between plural CPUs.

CONSTITUTION: Correspondingly to IOs 8, 9 to be controlled, the IOCs (input and output control devices) 11, 12 are respectively provided and a change over means 70 for selecting and connecting the respective IOCs 11, 12 so as to be commonly used between the plural CPUs 1, 2 is provided. The IO commonly using device 70 consists of a relay, an electronic relay or a change over element such as a connector. When the IO 8, the IO 9 are connected to the CPU 1, the connection bus to the CPU of the respective IOC 11, and the IOC 12 is connected to the bus of the CPU 1 by the IO commonly using device 70. Thereby, the respective IOCs 11, 12 are not disposed in the plural CPUs 1, 2 to make the constitution of a hardware economical.