When LPAR in a physical computer is migrated to LPAR in another in the state that OS operates, OS in LPAR can access disk which the OS has accessed before migration just after migration. FC-HBAs connected to the physical computers of the source and destination are constructed redundantly and one FC port is set to logging-out state in migration source before resumption of OS on the way of migration. After logging-in processing of FC is performed beforehand in migration destination by means of WWN of FC logged out in migration source, processing is performed so that path between FC logged and disk is viewed as being on-line from only OS. Path between FC not logged at destination and disk is processed to be viewed as being off-line from OS just after OS operates at destination, so that OS at destination can access the disk.