PURPOSE: To attain the effective use of register area within a recording medium by controlling information in serial numbers and in the order of the data area registration to the same recording medium and performing the unitary control of the registered pointer information in serial number for each file.

CONSTITUTION: A disk recording medium is divided into an index area 1 and a data area 2. In the area 1 information is written in order on each file F with no physical division. This writing order is coincident logically with the register order R1Wm to the area 2. Each data is subindexed into file numbers F1W and intra-file serial numbers r1W against the order R1Wm to the area 2. Then these numbers are mixed together. For instance, a serial number R4, a file F1, an intra-file serial number r1 and the attribute information related to the number R4 are written to a new register index area 24 of a format 23 of the index information divided for each file. While a serial number R2 and an intra- file serial number r1 are written on the file F1 of the pointer information 23 registered on each file.