PURPOSE: To register a sub file by reconstituting a library file when a logical area is lacked in the case of registering the sub file on the library file.

CONSTITUTION: This system is composed of a sub file registration size detection part 2 for detecting the size of the sub file to be registered, sub file registration position detection part 3 for retrieving the empty area of the library file or deciding the registration position of the sub file, library file reconstitution part 4 for reconstituting the library file when there is no empty area, and sub file registration part 5 for registering the sub file at the position decided by the sub file registration position detection part 3.