An embodiment dialogue system includes a speech recognizer configured to convert an utterance of a user into an utterance text, a natural language understanding module configured to identify an intention of the user based on the utterance text, and a controller configured to generate a first control signal for performing control corresponding to the intention of the user, identify whether an additional control item related to the control corresponding to the intention of the user exists, and in response to the additional control item existing, generate a second control signal for displaying information about the additional control item on a display.