PURPOSE: To provide a means enhancing the efficiency of file transfer between server and client and to make this efficiency enhancing means to apply to file transfer between spots with a time difference.

CONSTITUTION: A client 10 is provided with a final transfer date table 11 of the date receiving the transfer of a file 12 and a means sending back the file name and the final transfer date by pairing at the time of a file transfer request. The server 20 is provided with an update date table of the date updating a file 22 and a means comparing an update date and a final transfer date at the time of receiving the file transfer request and processing a transfer request. Besides, in order to slove the problem on the time difference, the client 10 is provided with a table holding the time difference between the client and the server 20.