A file server which is a local file server, wherein the filer sever is coupled to a communication network and via the communication network to a remote file server and is operable to manage a local storage device, the file server comprising: a first communication interface device configured to be coupled to the communication network; a second communication interface device configured to be coupled to each of a plurality of user terminals for sending an access request that is either a read request or a write request specifying a file, and receiving the access request from each of the user terminals; and a processor configured to be coupled to the first and second communication interface devices, wherein the second communication interface device is configured to be coupled to each of the user terminals such as to receive an open request before the read request, and receive a close request after the read request, wherein the processor is configured to: replicate files which are replication targets in the local storage device to the remote file server managing a remote storage device; manage the replicated files, which are the files from which data is replicated, as deletable migration target files without deleting from the local storage device in a case where a first condition is satisfied; and update a count value of the migration target file in accordance with a first rule each time receiving the open request; and update the count value of the migration target file in accordance with a second rule each time receiving the close request; and delete a file of the migration target files from the local storage device when the file of the migration target files satisfies a second condition, wherein the second condition is that, after the updating of the count value of the migration target file is started, the count value becomes a specified value, and wherein the specified value is equivalent to the fact that the file is not referred to by any of the user terminals. a first communication interface device configured to be coupled to the communication network; a second communication interface device configured to be coupled to each of a plurality of user terminals for sending an access request that is either a read request or a write request specifying a file, and receiving the access request from each of the user terminals; and a processor configured to be coupled to the first and second communication interface devices, wherein the second communication interface device is configured to be coupled to each of the user terminals such as to receive an open request before the read request, and receive a close request after the read request, wherein the processor is configured to: replicate files which are replication targets in the local storage device to the remote file server managing a remote storage device; manage the replicated files, which are the files from which data is replicated, as deletable migration target files without deleting from the local storage device in a case where a first condition is satisfied; and update a count value of the migration target file in accordance with a first rule each time receiving the open request; and update the count value of the migration target file in accordance with a second rule each time receiving the close request; and delete a file of the migration target files from the local storage device when the file of the migration target files satisfies a second condition, replicate files which are replication targets in the local storage device to the remote file server managing a remote storage device; manage the replicated files, which are the files from which data is replicated, as deletable migration target files without deleting from the local storage device in a case where a first condition is satisfied; and update a count value of the migration target file in accordance with a first rule each time receiving the open request; and update the count value of the migration target file in accordance with a second rule each time receiving the close request; and delete a file of the migration target files from the local storage device when the file of the migration target files satisfies a second condition, wherein the second condition is that, after the updating of the count value of the migration target file is started, the count value becomes a specified value, and wherein the specified value is equivalent to the fact that the file is not referred to by any of the user terminals.