A driving assistant device includes: a detection unit configured to detect at least one of an edge of a road, a lane of the road, and an object positioned within a certain range on the road; a calculation unit configured to calculate distance from the edge, distance from the lane, distance from the object, and speed of the object, and to calculate time to collision (TTC) with each of the edge, the lane, and the object based on the calculated distances and speed; a management unit configured to set a risk level of at least each one of the edge, the lane, and the object, and to adjust the risk level based on the TTC; and a control unit configured to control at least one of an indicator, a steering system, a brake, a headrest, and a belt according to the risk level.