PURPOSE: To smoothly perform the file compressing work of information from first to last without interruption, by cancelling encoding of words whose frequency in appearance is low when a list (memory) is filled up at the time of encoding of words.

CONSTITUTION: Information entered in an input object file 1 is read out in order from the first and is transferred to and stored in an output object file, and words are extracted from the read input file. Information indicating substitution of a word with a number of the list is outputted to an output file 3 when the frequency in appearance of this word reaches a certain value, and only the number of the list is outputted to the output line and is copied when the same word is detected hereafter. If this word list is filled up, the word whose frequency in appearance is lowest is detected and is deleted and another word is registered to reuse the substitution number. Thus, many information are efficiently stored in the file in a short time.