1. A movement trajectory predicting device predicting a movement trajectory of an object around a vehicle, the device comprising: an object detection unit configured to acquires a position of the object around the vehicle; a speed acquisition unit configured to acquires a ground speed of the object; a relative movement vector calculation unit configured to calculates a relative movement vector of the object with respect to the vehicle by using speed information on the vehicle and the ground speed of the object acquired by the speed acquisition unit; a classification unit configured to records positions in the movement trajectory of the object acquired by the object detection unit and to classify the recorded positions into a plurality of groups based on the relative movement vector calculated by the relative movement vector calculation unit; and a movement trajectory prediction unit configured to predicts the movement trajectory of the object based on a plurality of positions of the object included in at least one of the groups classified by the classification unit.