As a practical information guidance system, we have been developing a speech-oriented system named "Takemaru-kun". The system has been operated on a public space since Nov. 2002. The system answers to user's question about the hall facilities, sightseeing, transportation, weather information around the city, etc. All triggered inputs to the system have been recorded since the operation started. And all system inputs during 22 months are manually transcribed and labelled for speaker’s gender and age category. In this paper, we conduct a long-term prosody analysis of user speech to find a clue to obtain user’s attitude from a user’s speech. In this preliminary analysis, it is observed that F0 decreases regardless of age and gender category when the stability of the dialogue system is not established.