PURPOSE: To shorten a maintenance processing time and to improve throughput by retrieving the index code of an erasing object while using any pecualiar key in the case of erasing the index record.

CONSTITUTION: When it is necessary to erase a corresponding index record 3 in the case of updating or erasing a data record 8 in relation between an index 1 and the data record 8, a key 4 and a pointer 5 of the index record 3 corresponding to the data record 8 of the erasing or updating object are coupled, the peculiar key is prepared to uniquely designate the data record 8 of the erasing or updating object, and the data record 8 of the erasing or updating object is erased with this peculiar key. Namely, since the real storage position of the corresponding data record 8 is shown concerning the pointer 5, all of the pointers 5 have different contents even when the key 4 is same.