DESCRIZIONE
A method for a collision risk calculation includes: executing acquisition processing that includes acquiring travel information regarding a position and velocity of each of a first vessel and a second vessel; executing region calculation processing that includes calculating a region having a possibility of future collision between the first vessel and the second vessel from the travel information of each of the first vessel and the second vessel; and executing first risk calculation processing that includes calculating a first risk value based on a maneuvering amount used by the first vessel or the second vessel in order to avoid the region.