PURPOSE: To provide the disk cache controller for a virtual disk which generates no difference in access speed from an actual machine.

CONSTITUTION: A detecting means 2 confirms the DIR, FAT, etc., of an actual disk when a virtual computer is actuated, and detect discontinuous data blocks on the actual disk among respective data blocks of a virtual disk. A cache input/output means 13 handles those data blocks so that actual successive data blocks are held in a cache preferentially. For example, they are expelled from the cache if there is not access 30 times although the data blocks are normally expelled if there is not access 10 times, or never expelled from the cache.