1. A driving assistance device mounted on a vehicle and displaying a condition around the vehicle on a display unit, the driving assistance device comprising: a storage device that stores an external shape of the vehicle; an object detection device that detects a position of an object disposed around the vehicle and an external shape of only a vehicle-facing side of the object; a movement information acquiring device that acquires movement information relating to a direction and an amount of movement of the vehicle; a relative position estimating device that estimates a relative position of the object to the vehicle based on the position of the object acquired in the object detecting device and the movement information acquired in the movement information acquiring device; an image generating device that generates a top-view image of the vehicle and the object viewed from above the vehicle based on the external shape of the vehicle, the external shape of only the vehicle-facing side of the object, and the relative position of only the vehicle-facing side of the object to the vehicle; a display device that displays the top-view image on the display unit; and an object generating device that generates an object image indicative of the external shape of the object based on the external shape of the object detected in the object detecting device, wherein: the storage device stores a vehicle image indicative of the external shape of the vehicle; and the image generating device generates the top-view image including the object image and the vehicle image.