To make it possible to generate a response sentence with respect to an input speech sentence without preparing a large amount of data.
A response-type determining unit 117 determines, based on an analysis result of a speech sentence analyzed by a speech-content analyzing unit 112, a speech type indicating a type of the speech sentence and determines a response type with respect to the determined speech type based on the speech type and a type conversion rule prescribing, for each speech type, a rule for a response type with respect to a speech of the speech type. A response-sentence generating unit 119 generates the response sentence based on the response type and a response sentence database.