PURPOSE: To convert the constitution generation of a record without interrupting data base service by providing a record header part with record constitution generation information and a directory with a record conversion code for conver sion between an old and a new generation.

CONSTITUTION: A record processing part 4 when receiving a request for record retrieval or update from a user reads the conversion code out of the directory 2 by a loading means 8 and loads the conversion code in conversion code area 9. Then a necessary record is read out of the data base 1 to a record buffer 5. Then the record processing part 4 checks the number of the header part of the record in the record buffer 5 to specify the constitution generation of the record. When the record of a read generation is a record to be converted, a record of older constitution generation than the conversion code is converted into the record of the new generation constitution. After the conversion, the record is updated to rewrite the data base 1, so the constitution generation of the record can be converted without interrupting the service of the data base 1 temporarily.