PURPOSE: To reduce key input and to start a retrieving process for a partial solution by displaying predicted word candidates and allowing a user to make a choice.

CONSTITUTION: While the meaning of an inputted request sentence is analyzed at word/paragraph level, a partial syntax semantics tree is generated from the means of words and paragraphs which are obtained in order and matched against the semantic relation of a task to predict a word to be inputted next, thereby displaying predicted word candidates. Then a word that the user intends among the displayed word candidates is selected with a mouse 3, etc. In a halfway input stage of the request sentence, a word following it is predicted and displayed and it is inputted as an input sentence, so key input operation is reducible. Further, a partial solution can be retrieved in the middle of the request sentence and fast retrieval is enabled.