A method for navigating a ship, comprising: receiving a first position information and a second position information from a management server having a storage device for storing the first position information of a first ship and the second position information of a second ship wherein the first position information is received via a mobile telephone network from a user terminal used in the first ship and the second position information is transmitted via VHF radio from an AIS (Automatic Identification System) device used in the second ship and received via an AIS system, wherein the user terminal comprises a radar display module and a map display module; displaying an icon indicating the first ship at a position designated by the first position information on a nautical chart, and an icon indicating the second ship at a position designated by the second position information on the nautical chart; displaying a track of the first ship and a track of the second ship for a predetermined period from past to present; setting for each of said first and second ships a warning area as a fan-shaped area having a first center angle and a radius corresponding to a first distance in the moving direction of the first and second ships and setting a caution area as a fan-shape area having a second center angle larger that the first center angle and a radius corresponding to a second distance in the moving direction shorter than the first distance; and displaying a notification of caution or a notification of warning in a case where the caution area or the warning area of the first ship overlaps the caution area or the warning area of the second ship; displaying the notification of caution by the radar display module and the map display module when the caution area of the first ship and the caution area of the second ship overlap with each other; and displaying the notification of warning by the radar display module and the map display module when the warning area of the first ship and the warning area of the second ship overlap with each other, wherein an importance level and an emergency level of the notification of warning are higher than those of the notification of caution. receiving a first position information and a second position information from a management server having a storage device for storing the first position information of a first ship and the second position information of a second ship wherein the first position information is received via a mobile telephone network from a user terminal used in the first ship and the second position information is transmitted via VHF radio from an AIS (Automatic Identification System) device used in the second ship and received via an AIS system, wherein the user terminal comprises a radar display module and a map display module; displaying an icon indicating the first ship at a position designated by the first position information on a nautical chart, and an icon indicating the second ship at a position designated by the second position information on the nautical chart; displaying a track of the first ship and a track of the second ship for a predetermined period from past to present; setting for each of said first and second ships a warning area as a fan-shaped area having a first center angle and a radius corresponding to a first distance in the moving direction of the first and second ships and setting a caution area as a fan-shape area having a second center angle larger that the first center angle and a radius corresponding to a second distance in the moving direction shorter than the first distance; and displaying a notification of caution or a notification of warning in a case where the caution area or the warning area of the first ship overlaps the caution area or the warning area of the second ship; displaying the notification of caution by the radar display module and the map display module when the caution area of the first ship and the caution area of the second ship overlap with each other; and displaying the notification of warning by the radar display module and the map display module when the warning area of the first ship and the warning area of the second ship overlap with each other, wherein an importance level and an emergency level of the notification of warning are higher than those of the notification of caution.