PURPOSE: To recognize and manage transition for repeatedly generating or restoring the history of alarm generating status by sending the history information of the alarm generating status and error information in generation status detection from monitored devices to a monitoring device.

CONSTITUTION: When the monitoring device A poles the monitored devices B, C, the devices B, C latch the contents of a history information buffer D, clear the contents of a status transition flag register E and send the contents of an error flag register G and the buffer D to the device A. The device A adds the received information to data stored in a history information data base (a) and manages the stored data. At the time, the devices B, C clear the register G and unlatch the cleared buffer D. Thereby data generated from a status flag register F and the register E are set up in the buffer D.