Method for creating a language model capable of preventing deterioration of quality caused by the conventional back-off to unigram. Parts-of-speech with the same display and reading are obtained from a storage device (206). A cluster (204) is created by combining the obtained parts-of-speech. The created cluster (204) is stored in the storage device (206). In addition, when an instruction (214) for dividing the cluster is inputted, the cluster stored in the storage device (206) is divided (210) in accordance with to the inputted instruction (212). Two of the clusters stored in the storage device are combined (218), and a probability of occurrence of the combined clusters in the text corpus is calculated (222). The combined cluster is associated with the bigram indicating the calculated probability and stored into the storage device.