A correspondence relationship between keywords for instructing the start of a speech dialogue and modes of a response is defined in a response-mode correspondence table. A response-mode selecting unit selects a mode of a response corresponding to a keyword included in the recognition result of a speech recognition unit using the response-mode correspondence table. A dialogue controlling unit starts the speech dialogue when the keyword is included in the recognition result of the speech recognition unit, determines a response in accordance with the subsequent recognition result from the speech recognition unit, and controls a mode of the response in such a manner as to match the mode selected by the response-mode selecting unit. A speech output controlling unit generates speech data on the basis of the response and mode controlled by the dialogue controlling unit and outputs the speech data to a speaker.