PURPOSE: To remarkably content of data and to reduce the transmission time by transmitting a data train to a compressing and converting section and obtaining a compression value from a maximum value included in the data train and a calculated value in an operating section.

CONSTITUTION: An input data train ei is stored in an input data storage section 6, the data train ei is fed to the compression and converting processing section 7, and the maximum value M included in the data train ei is detected. The compressing value V is obtained by this maximum value M and the calculated value in the operating section 8, these values M, V are transmitted to an output buffer section 10 or a storage holding section 11 and transmitted to a communication line. Then, the data compressed by this compressing system is read from a file 13 via the communication line and stored in an input data storage section 14. The compressing data comprising the stored maximum value M and compressed value V is fed to a restoration processing section 15, the processing section and the operation section 16 perform restoring processing, and the restored data is stored in a data section 18.