PURPOSE: To fairly and efficiently extract key words.

CONSTITUTION: An input means 1 converts a type part except graphics and charts, etc., to a readable form by utilizing an OCR or the like. A data extraction part 12 reads data from the input means 1 and outputs a key word candidate from a dictionary provided beforehand and the predetermined kinds of stop words. A data maintenance part 13 retreives a data holding part 5 relating to the extracted key word candidate, newly stores the key word candidate in the data holding part 5 when it is not present on the data holding part 5 and increases the appearance number of time of counter of the key word candidate by '1' when it is present. An output part 14 outputs the key word candidate for which the value of the appearence number of times of counter of the extracted key word is more than a predetermined value as the key word.