PURPOSE: To prevent the system from entering a down state owing to abnormality of an external storage device by transferring system data from a monitor device after performing actuation by reading characteristic information required for the actuation out of a nonvolatile memory.

CONSTITUTION: Respective communication controllers 100-1 to 100-n load the characteristic information required for the actuation in the nonvolatile memory 800 from he external storage device 700 and stores it in advance. Then if the device 700 becomes abnormal at the time of power recovery after a break of power supply, the devices 100-1 to 100-n read the characteristic information required for the actuation out of the memory 800 and performs the actuation, and then informs the monitor device 300 of that. The device 300 transfers the necessary system data to the devices 100-1 to 100-n so as to make a communication among the communication controllers. Consequently, the system data are automatically restored to prevent the system down and the reliability of the communication network system can be improved.