16. The device of claim 10 , wherein the extractor extracts second inquiry search words excluding the first inquiry search word from at least one of the search word history and the webpage information, and the relation value calculator calculates similarity value between the first inquiry search word and each of the extracted second inquiry search words based on a frequency of each of the second inquiry search words in at least one of the search word history and the webpage information, selects a third inquiry search word from the second inquiry search words, which is to be included in a first similar search word group together with the first inquiry search word, based on the similarity value; and revises the calculated relation value between the first inquiry search word and each of the answer candidate keywords of the first inquiry search word based on a relation value between the third inquiry search word and each of answer candidate keywords of the third inquiry search word.
16. The device of claim 10 , wherein the extractor extracts second inquiry search words excluding the first inquiry search word from at least one of the search word history and the webpage information, and the relation value calculator calculates similarity value between the first inquiry search word and each of the extracted second inquiry search words based on a frequency of each of the second inquiry search words in at least one of the search word history and the webpage information, selects a third inquiry search word from the second inquiry search words, which is to be included in a first similar search word group together with the first inquiry search word, based on the similarity value; and revises the calculated relation value between the first inquiry search word and each of the answer candidate keywords of the first inquiry search word based on a relation value between the third inquiry search word and each of answer candidate keywords of the third inquiry search word. 17. The device of claim 16 , wherein the relation value calculator revises the similarity value between the first inquiry search word and each of the second inquiry search words based on a number of inquiry search words commonly existing in the first similar search word group and a second similar search word group of each of the second inquiry search words, and selects the third inquiry search word based on the revised similarity value.