To execute conversion to related words concerning words and phrases extending plural segments without complicated operation by a user by extracting an entry word even when the object of conversion is a word/phrase constituted by combining two segments and dictionary-retrieving this so as to convert to a desired synonym.

An entry word is extracted even when the object of conversion is a word/phrase constituted by combining two segments and this is dictionary- retrieved so as to convert to a desired synonym. Related information is retrieved by segmenting the combination of a designated clause and another clause as an entry word when converting instruction to a related word is given, and retrieving related word information stored in a dictionary, etc., based on this entry word. At this device, a prescribed segment is selected and a synonym conversion executing key is operated by a user, a KANA/KANJI mixed character string corresponding to a selected segment is transferred from a segment divide-writing conversion module BW to a synonym conversion module DH.