To provide a data base system that can maintain interchangeability with an old system of a backed up data base file and interchangeability with a new system of a data base file backed up by the old system.

A data base system that has a first data base for storing plural first data is composed of a first data read means 4 for reading the first data outside a security protection object from the first data base, a substitute data storage means 6 for storing the second data for substituting security object data, and a first data base preparation means 8 that prepares the second data base on the basis of the second data stored in the substituted data storage means 6 in place of the first data outside the security object which the first data read means 4 reads and the data to be the security object data in the data base.