PURPOSE: To extract history information even if a fault is generated in a body and to reduce the load of a CPU by accumulating the history information formed by a service processor in an external memory device connected to the service processor.

CONSTITUTION: When a message is outputted from a body 1 to a system console (CONSL)7, the service processor (SVP)6A combines the time information of a timer (TOD)21 with the message to form a history information element and stores the element in the external memory device (FDD)22 or the 2nd external memory device (FXD)23. When a message is transferred from the CNSL7 to the body 1, the time information of the TOD21 is combined with the message to form the history information and the information is accumulated in the FDD22 and the FXD23. Necessary information can be read out from the history information file without passing through the body 1.