To shorten the break time of a service at the time of system down by transferring data, which are copied to the main storage device of a reserve system by a preservation processing part, to an external storage device with a freeze damp processing part.

In a preservation processing part 12, it is discriminated by a reserve system MM information discriminating means 120 whether a main storage device 2 of the reserve system at that time is in active state or inactive state. In the case of inactive state, stored contents in a main storage device 2 (#0) of an active system are copied to a main storage device 2 (#1) of that reserve system by a copying means 121. When preserving processing is finished, an initial active system memory setting part 13 is driven, the main storage device 2 (#0) of the active system is initially set and online processing is started by an online start part 14 while using the initially set main storage device 2 (#0). Continuously, a freeze damp processing part 15 is driven and data stored in the main storage device 2 (#1) of the reserve system are transferred to an external storage device 3.