An autonomous travel assistance device mounted on each of an own vehicle and another vehicle, wherein the map used in the navigation system of the own vehicle and the map used in the navigation system of the other vehicle include a plurality of common position reference points (Mr), the autonomous travel assistance device comprising: - processor; - a storage unit (902, 903, 901) to store position reference point data including identification information of a position reference point being set at a junction at which traffic lanes join or at a diverging point at which the traffic lanes diverge in an intersection area where the traffic lanes intersect, join, or diverge and an absolute position information of each of a plurality of the position reference points that is common to the own vehicle and the another vehicle; - a receiving unit as a receiver of a communication device to receive from the other vehicle the identification information of the position reference point (ID Mr) that is an immediately near position reference point positioned in the traveling direction of the other vehicle, and a relative position of the other vehicle to the absolute position information of the position reference point; and - a specification unit of a vehicle position information processing unit to acquire the absolute position information of the position reference point from the position reference point data on the basis of the received identification information of the position reference point and to specify a position of the other vehicle on the basis of the acquired absolute position information of the position reference point and the received relative position of the other vehicle, wherein the received relative position of the other vehicle is expressed by using a distance (d) between the position reference point in the absolute position information and the position of the other vehicle in a length direction of a road in the same intersection area of the own vehicle and an offset, the offset being a distance between the position reference point in the absolute position information and the position of the other vehicle in a width direction of the road, wherein the vehicle position information processing unit provides the specified position of the other vehicle to a vehicle control system of the own vehicle, that controls the own vehicle on the basis of the position of the other vehicle specified by the vehicle position information processing unit and the position of the own vehicle measured by a positioning system in order to avoid collision between the own vehicle and the other vehicle. - processor; - a storage unit (902, 903, 901) to store position reference point data including identification information of a position reference point being set at a junction at which traffic lanes join or at a diverging point at which the traffic lanes diverge in an intersection area where the traffic lanes intersect, join, or diverge and an absolute position information of each of a plurality of the position reference points that is common to the own vehicle and the another vehicle; - a receiving unit as a receiver of a communication device to receive from the other vehicle the identification information of the position reference point (ID Mr) that is an immediately near position reference point positioned in the traveling direction of the other vehicle, and a relative position of the other vehicle to the absolute position information of the position reference point; and - a specification unit of a vehicle position information processing unit to acquire the absolute position information of the position reference point from the position reference point data on the basis of the received identification information of the position reference point and to specify a position of the other vehicle on the basis of the acquired absolute position information of the position reference point and the received relative position of the other vehicle, wherein the received relative position of the other vehicle is expressed by using a distance (d) between the position reference point in the absolute position information and the position of the other vehicle in a length direction of a road in the same intersection area of the own vehicle and an offset, the offset being a distance between the position reference point in the absolute position information and the position of the other vehicle in a width direction of the road, wherein the vehicle position information processing unit provides the specified position of the other vehicle to a vehicle control system of the own vehicle, that controls the own vehicle on the basis of the position of the other vehicle specified by the vehicle position information processing unit and the position of the own vehicle measured by a positioning system in order to avoid collision between the own vehicle and the other vehicle.