To improve HDD performance by performing effective cache processing with respect to different file systems.

An MBR is read out from a magnetic disk 121, and the read-out MBR is stored in a sector buffer 307 by an event handler 304. A segment control part 302 acquires the MBR stored in the sector buffer 307 and identifies a file system by referring to a partition type field. The segment control part 302 refers to a cache mode table 305, and in the subsequent read and write processes to determine a cache mode corresponding to the file system stored in the MBR, the segment control part 302 performs buffer handling and command execution control in accordance with the determined cache mode. By selecting the suitable cache mode in accordance with the file system, performance can be improved.