A correct collision judgment is realized between an obstacle and a vehicle even when the vehicle enters a curve. In a collision judgment apparatus for judging the collision between the vehicle and the obstacle based on a relative positional relationship between a subject vehicle position of the vehicle and a relative movement straight line of the obstacle with respect to the vehicle as calculated based on a plurality of pieces of the position information acquired by a position information acquiring unit in relation to the obstacle, the relative positional relationship between the relative movement straight line and the subject vehicle position is adjusted so that a distance between the relative movement straight line and the subject vehicle position is separated if it is judged that the vehicle enters an entrance to a curve as compared with a situation in which the vehicle does not enter the entrance to the curve.