3. The target estimation device according to claim 2 , wherein the item and each of the function expressions stored by said function storing unit further include at least a word indicating an operation action for the operation object, and said intention calculating unit is configured to use the calculation method that assigns more weight to a semantic similarity between a word that indicates the operation object and is included in an item, and a function expression including a word that indicates the operation object and a word that indicates the operation action than a semantic similarity between a word that indicates the operation action and is included in the item, and the function expression including the word that indicates the operation object and the word that indicates the operation action.
2. The target estimation device according to claim 1 , wherein the item and each of the function expressions include at least a word indicating an operation object, the function expressions being stored by said function storing unit, and said intention calculating unit is configured to calculate the degree of the intention using a calculation method that assigns more weight to the word indicating the operation object from among the plurality of words included in the item, when the category detected by said identical word detecting unit is an operation object.