There is provided a navigation system, comprising: a buoy on a water surface movably anchored to a bottom; a plurality of at least three transmitters fixed to the bottom or at different positions in the water for transmitting signals to specify the positions; a receiver, being disposed with the buoy, configured to receive signals transmitted by the plurality of transmitters; a signal processor, being disposed with the buoy, configured to specify the position of the buoy, based on the signals received by the receiver, and generate a navigation signal indicating the position of the buoy, and a radio, being disposed with the buoy, configured to transmit the navigation signal generated in the signal processor wirelessly, the navigation signal being receivable by a radio in a mobile body.