To safely store snapshot data by disconnecting a disk and making a copy reservation even if an in-operation system of a dual system operates abnormally or is misoperated.

This system is equipped with a means which performs operation/ non-operation control over an application program 13 in operation by a 1st computer 1, a means which controls writing to a 2nd storage part 34 where a 1st storage part 33 of a disk device stored with processing information of the application program 13 in operation is backed up, a means which makes a reservation while writing to the 2nd storage part 34 is inhibited so that information stored in the 2nd storage part 34 is copied and transferred as snapshot data, and a means which copies and transfers the data.