To provide a technology for easily performing the migration of data stored in an original hard disk to a new hard disk to be switched at the time of removing a hard disk mounted on a computer, and attaching a new hard disk.

This data migration system is provided with a client mounted with a first storage device and a server connected through a network to a client, and the client transmits data stored in the first storage device through the network to the server by associating the data with the identification information of the client, and the server stores the received data. Afterwards, when the first storage device is removed, and a second storage device is mounted, the client reads the data associated with the identification information from the server, and copies the data to the second storage device based on the identification information according to a program for data migration stored in the second storage device.