A navigation system (20) includes a transceiver unit (210), a display unit (250), an input unit (260) and an ECU (230). The transceiver unit (210) transmits a signal for demanding a detection of a navigation path to a path detecting server (10) and then receives path data which represent the navigation path from the path detecting server (10). The display unit (250) outputs the navigation path or a revised navigation path. The ECU (230) conveys data on a departure point and a destination from the input unit (260) to the transceiver unit (210) and transfers the path data from the transceiver unit (210) to the display unit (250). Further, the ECU (270) precalculates deviation-expected paths in the course of driving along the navigation path and selects the revised navigation path among the precalculated deviation-expected paths in case a present position of a mobile object deviates from the navigation path to thereby provide the revised navigation path to the display unit (250).