We propose a speech input interface for the Mobility Support Geographic Information System (GIS). This GIS can provide optimal paths to destinations with information on barrier and barrier-free objects related to sidewalks for all pedestrians, especially elderly people and disabled people. We have created a speech input interface for the GIS, and evaluated it for elderly people. Results indicated that speech input is much easier than mouse input for them, especially for half of them who have difficulty in using PCs. We also investigated elderly peoples' behavior toward a dialog system by using Wizard of Oz. In this experiment, we applied several dialog styles, user-initiated, system-initiated, with/without the application. Experiment results show that their behavior is dependent on their own experience with computers.