The present invention includes a morpheme extracting unit 420 configured to extract, based on a character string corresponding to input information, at least one morpheme constituting a minimum unit of the character string, as first morpheme information, a topic search unit 340 configured to compare the first morpheme information extracted at the morpheme extracting unit 420 with topic titles, and to search a topic title corresponding to the first morpheme information from among the topic titles, and a reply retrieval unit 350 configured to retrieve, based on the topic title searched at a topic identification information search unit 320, a reply sentence associated with the topic title.