A syntactic analysis unit 104 performs a syntactic analysis for linguistic information on acquired user speech. A non-linguistic information analysis unit 106 analyzes non-linguistic information for the acquired user speech, the non-linguistic information being different from the linguistic information. A filler length determination unit 120 determines a length of a filler according to a non-linguistic information analysis result. A filler generation unit 130 generates a filler having a length corresponding to a result of a determination by the filler length determination unit 120. The filler length determination unit 120 determines that a long filler should be generated when a syntactic analysis result needs to be used to generate a response and, otherwise, determines that a short filler should be generated. The voice output unit 150 outputs the response generated by the response generation unit 140 after outputting the filler.