PURPOSE: To secure DASD (direct access storage device) data even in the case of the occurrence of a fault on the way of writing from a host computer by setting the end flag of a present record at the time of the end of writing of the present record.

CONSTITUTION: Even if the write end position is not written in the directory of a non-volatile memory 15b by occurring the fault on the way of the writing from the host computer, an end bit 3 as the end flag of a record counting part whose write is terminated just before the occurrence of fault is set. Therefore, the end position to be recorded back on the DASD 20 is recognized and the recorde to the is end position written back to a DASD 20, and DASD data is secured.