A vehicle trajectory calculation method is provided. In the vehicle trajectory calculation method, a travel trajectory of a vehicle in a travel route is calculated based on a GPS signal received at predetermined time intervals with a GPS receiver of the vehicle during traveling. When there is an unmeasurable section where the travel trajectory cannot be normally calculated based on the GPS signal, the travel trajectory in the unmeasurable section is calculating by performing an interpolation based on the calculated travel trajectories in sections anterior to and posterior to the unmeasurable section.