We propose a method for extracting information on the technical effect from a patent document. The information on the technical effect extracted by our method is useful for generating patent maps (see e.g., Figure 1 .) automatically or analyzing the technical trend from patent documents. Our method extracts expressions containing the information on the technical effect by using frequent expressions and clue expressions effective for extracting them. The frequent expressions and clue expressions

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... are extracted by using statistical information and initial clue expressions automatically. Our method extracts expressions containing the information on the technical effect without predetermined patterns given by hand, and is expected to be applied to other tasks for acquiring expressions that have a particular meaning (e.g., information on the means for solving the problems) not limited to the information on the technical effect. Our method achieves not only high precision (78.0%) but also high recall (77.6%) by acquiring such clue expressions automatically from patent documents.