The invention provides a communication control method for switching paths at high speed to switch storages without a special path switching means in a host computer, without stopping an application or without changing settings, and a device for realizing the same. The present computer system comprises a host computer 20, a storage devices 10 connected via a network 30 to the host computer 20, and a name server 40, wherein the host computer 20 has a function to search for an alternate path when a defect is discovered in a path used for connection with the storage 10, and the storage device 10 has a target communicating with the host computer 20 through a port, a registration change means for changing a registered address associated with the registration of a migration source target registered in the name server 40 to an address of a migration destination port, and a means for disconnecting all communication means established with the migration source target subsequent to the registration change process.