PURPOSE: To eliminate the need of complexed processing on the application program side by performing the address calculation of a direct edition file collectively by an I/O processing part.

CONSTITUTION: In writing or reading-out data in/from a direct edition file 3, an application program 1 requests write or read-out to an I/O processing part 2. At that time a file name and the value of a record key are supplied to the I/O processing part 2. After receiving the read-out/write request, the I/O processing part 2 finds a block number calculation routine from the file name and transfers the control to the block number calculation routine. If a block number calculation routine 5-a is selected, the routine 5-a finds the block number from the record name and sends the calculated value to the I/O processing part 2. The I/O processing part 2 accesses readout or write to the direct edition file on the basis of the block number.