To provide a chat system allowing a chat using the Internet to develop into arbitrary conversation in addition to previously prepared conversation, and capable of executing promotion of a commodity/service to a consumer, or collection of needs or taste of the consumer in development of the commodity, sales or the like in the chat without imparting incongruity to a user of the chat.

This chat system has a keyword retrieval means executing keyword retrieval by use of a DB storing even information collected from a Web of the Internet in real time in addition to general-purpose information when a keyword cannot be extracted, and a query sentence generation means generating a query sentence transmitted to the user when the keyword cannot be extracted even by the keyword retrieval means, in addition to a character speech content decision means extracting a reply sentence from a conversation DB by the keyword extracted by morpheme analysis of a conversation sentence inputted by the user.