To prevent the loss of a received message unrelated with the failure due to software in a hot stand-by system.

A master system central processing unit 4 stores a received message in a recovery file 6, and operates processing of this message. At the time of detecting an abnormal end state due to software when processing the received message, the master system central processing unit 4 obtains the revision of a load module in an executing state and an abnormal end address, and communicates this information to a slave system, and then operates down processing. At the time of detecting the down state of the master system central processing unit 4, a slave system central processing unit 5 moves to a new master system, and processes unprocessed received messages other than the received message being the cause of the abnormal end among unprocessed received messages stored in the recovery file based on the revision of the load module and the abnormal end address communicated from the master system central processing unit 4.