PROBLEM TO BE SOLVED: To permit speech understanding more powerfully and accurately than a conventional example, and moreover, to detect a combined concept having restriction in combination with high accuracy. SOLUTION: A decision tree generation processing part 21 generates a 1st decision tree for deciding whether or not plural meaningful concepts and a combination of concepts are contained in a spontaneous speech sentence based on the study data of the spontaneous speech sentence, and a 2nd decision tree for deciding whether or not an utterance action exists. The speech action and combined concept decision part 23 make the above-mentioned decision for the inputted spontaneous speech sentence by using the 1st and 2nd decision trees, and output a result of the decision. An argument decision part 24 enumerates argument names from the argument names stored beforehand based on the result of the decision; analyzes the syntax by using a partial sentence analysis rule corresponding to the enumerated argument name, and outputs the argument values corresponding to the spontaneous speech sentence by an intermediate language expression by arranging the corresponding argument values of the rule used.
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