To communicate a file between systems where the forms of handled files are different.

In the case of communication of, e.g. a JPEG picture file among systems 1A, 1B, 1C, the transmitter side system 1A transmits the picture file to a server 3, the server 3 stores the picture file, and the server 3 transmits the picture file to the receiver side systems 1B, 1C. In the case of receiving the picture file from the transmitter side system 1A, the server permits any JPEG compression form desired by the transmitter side system 1A, receives picture files 21, 23 or 25 with the JPEG compression form desired by the transmitter side system 1A and stores the received picture file in a proper JPEG compression form. When transmitting picture files 51, 52 or 55 stored in the sever 3 to the receiver side systems 1B, 1C, the server converts the form of the transmitted picture file into a JPEG compression form handled by the receiver side systems 1B, 1C and transmits the resulting picture file to the receiver side systems 1B, 1C.