In a driving assistance device, a distance information is acquired based on an image acquired by an imaging device mounted on a vehicle. The distance information includes a relative distance of a preceding vehicle in a travelling direction of the own vehicle, relative velocity thereof, and acceleration information thereof including relative acceleration. A time required until the own vehicle collides with the preceding vehicle is calculated with consideration of the acceleration information as a predicted collision time. It is determined whether or not the preceding vehicle is in a deceleration state by using the relative velocity. Further it is determined whether or not a collision possibility between the own vehicle and the preceding vehicle exists, and it is also determined to use the predicted collision time on the condition that the preceding vehicle is determined to be in the deceleration state and the collision possibility is determined to exist.