PURPOSE: To easily attain data compression without new development of data compression system by replacing the arrangement of high-order byte and low- order byte of each other order of characters in Japanese language characters among data to be compressed.

CONSTITUTION: The compressor consists of a data arrangement conversion section 20 replacing the arrangement of high-order byte and low-order byte of each other order of characters in Japanese language characters among data 10 to be compressed and a data compression section 30 storing a pattern of a consecutive byte data in the data to be compressed, compressing patterns with a high frequency of occurrence into a short data and outputting the result as a compression data 40. Thus, when arrangement of same data, 24H,24H appears, since a short data is allocated to the pattern, the data is easily compressed.