An object of the present invention is to reduce an operational load of a user who performs a voice input. In order to achieve the object, a user interface system according to the present invention includes: an estimation section 3 that estimates an intention of a voice operation of the user, based on information related to a current situation; a candidate selection section 5 that allows the user to select one candidate from among a plurality of candidates for the voice operation estimated by the estimation section 3; a guidance output section 7 that outputs a guidance to request the voice input of the user concerning the candidate selected by the user; and a function execution section 10 that executes a function corresponding to the voice input of the user to the guidance.
