PURPOSE: To improve the hit rate for sequential access by detecting sequential access and reading data in advance at the time of detecting it.

CONSTITUTION: A management table 5 of a cache memory 4 is provided with flags, and the flag corresponding to the block read by an advance read means 34 is set. When blocks whose flags are set are hit by following access of a transfer means 31, execution of sequential access is judged by an access mode deciding means 33, and following blocks are read in advance again by the advance read means 34. That is, the access mode deciding means 33 judges whether the data transfer element is sequential access or not; and is the case of the sequential access mode, the advance read means 34 reads data from a disk device 2 as the external storage device to a cache memory 4 in advance.