1. A language understanding device comprising: a language understanding model storing unit configured to store, as a language understanding model, word transition data including pre-transition states, input words, predefined outputs corresponding to the input words, word weight information, and post-transition states, and concept weighting data including concepts obtained from language understanding results for at least one word, and concept weight information corresponding to the concepts; a finite state transducer processing unit configured to output understanding result candidates including the predefined outputs based on words included in a word sequence being input and present states, and in accordance with the word transition data read out from the language understanding model storing unit, to accumulate word weights so as to obtain a cumulative word weight, and to sequentially perform state transition operations by which transitions to the post-transition states are carried out; a concept weighting processing unit configured to accumulate concept weights, which correspond to the concepts included in the understanding result candidates output from the finite state transducer processing unit, in accordance with the concept weighting data read out from the language understanding model storing unit so as to obtain a cumulative concept weight; and an understanding result determination unit configured to determine an understanding result from the understanding result candidates by referring to the cumulative word weight and the cumulative concept weight.