Abstract: A navigation supporting display apparatus makes it easy for an operator of ship to navigate with a safe passing distance between own ship and a target by indicating an exact danger area between own ship and the target ship. The apparatus has a collision point calculator which calculates a possible collision point of each of the vertexes of a polygonal safe passing region set around own ship, and the target ship, from a relative position of the target ship, a velocity vector of the target ship and a velocity of own ship. The apparatus has an own-ship-mapping-position calculator which calculates a position at which own ship would be located when each of the vertexes places on the collision point, and defines the position as a own-ship-mapping-position. The apparatus further has a danger area calculator which determines lines joining own-ship-mapping-positions corresponding to the collision points with each other to define a danger area.