To provide a shortest-course simulator in which simulation results can be executed in a short time utilizing simulation results obtained in previous run, when the shortest course of a road network is simulated.

When a current position is reset by a current position setting means 3, a correcting/initializing means 12 initializes work data stored in a work data storage means 7, such that only the data concerning a partial course starting from an altered current position is left as it is based on the data of simulation results of a shortest-course starting from a current position already stored in a storage means 8. When the work data, corrected/initialized by the correcting/initializing means 12, exists in the work data storage means 7, a shortest course simulation means 6 simulates a shortest course starting from the current position over a range which excludes the corrected/initialized work data.