To provide the data transfer relay system by which legality of a file in an internal storage device of a computer in operation is enhanced and the file transfer time is reduced.

Once a file transfer relay section 310 has received a transfer request of data 202 from a file transfer request system 101, the section 310 transfers the data 202 to the data transfer relay system so as to be stored in an internal storage device 320. If data 212A likely to be requested for transfer are not stored in the internal storage device 320, the data 212A are transferred to be stored in the internal storage device 320. In the case the data 212A are stored in the internal storage device 320, a file transfer system 211 confirms the validity of the data 212A. Only when the data 212A in the internal storage device 320 differ from the data 212A in the computer 210, a transmission request for the data 212A is performed to store the data to the internal storage device 320.