PURPOSE: To prevent the misretrieval of character strings by retrieving a charac ter string to be stored in a character string store part via a retrieving process part out of those character strings stored in a subject document store part.

CONSTITUTION: A control part 1-2 performs the control to convert a character string and a subject document inputted via an input part 1-1 into each standard form via a character string conversion part 1-4. Thus the input character string is converted into a standard form and stored in a character string store part 1-5. Then the subject document is also converted into a standard form and stored in a subject document store part 1-6. A retrieving process part 1-7 retrieves a character string to be stored in the part 1-5 out of those character strings stored in the part 1-6. Then the retrieved character string is displayed at a display part 1-8. In such a constitution, a desired character string can be retrieved with no omission.