1. A file-sharing system comprising: a file server connected to a client terminal via a first network, the file server including a first storage section in which at least one first real file system is stored and a cloud computing environment connected to the file server via a second network, the cloud computing environment including a second storage section in which at least one second real file system is stored, wherein the file server comprises: a file service providing section that provides a virtual file system, which is generated by virtually merging the first real file system and the second real file system, to the client terminal; a migration processing section that migrates one or more files between the first real file system and the second real file system in accordance with a predetermined condition; an object management section that manages correspondence relationships among each file or directory in the virtual file system, and each file or directory in the first real file system and the second real file system, the object management section further manages a batch processing flag indicating whether or not all of migrated files are to be processed by the cloud computing environment, when all files included in any directory in the first real file system have been migrated to the second real file system; and a first scan processing section that scans a file included in the first real file system to generate predetermined information, the first scan processing section is configured to be capable of updating the batch processing flag, wherein the cloud computing environment comprises: a second scan processing section that scans a file included in the second real file system to generate predetermined information, and wherein, when scan processing to any one or more target files or directories included in the virtual file system is started, the first scan processing section executes scan processing to the one or more target files included in the first real file system, the first scan processing section refers to the batch processing flag managed by the object management section, and when the batch processing flag indicates that all of the files included in one of the one or more target directories in the virtual file system are to be processed by the cloud computing environment, the first scan processing section sends a scan processing request to the cloud computing environment to execute scan processing to each file included in one of the one or more target directories, when the batch processing flag indicates that all of the files included in one of the one or more target directories in the virtual file system are to be processed by the cloud computing environment and when it would take a long time until the processing is completed by the cloud computing environment, the first scan processing section updates the batch processing flag, so that it indicates that all of the files included in one of the one or, more target directories in the virtual file system are not to be processed by the cloud computing environment, when the batch processing flag indicates that all of the files included in one of the one or more target directories in the virtual file system are not to be processed by the cloud computing environment, the first scan processing section executes scan processing to each file which is included in one of the one or more target directories and has been migrated to the second real file system, the second scan processing section executes scan processing to each target file in response to the instructions of the scan processing request, and sends the scan processing result to the file server, and the first scan processing section merges the scan processing result obtained with the first scan processing section and the scan processing result obtained with the second scan processing section, and records the merged result.