A driving support system comprising first and second UHF (Ultra High Frequency) roadside apparatuses and an in-vehicle unit mounted in a vehicle, wherein each UHF roadside apparatus includes: a UHF transmission part which is adapted to transmit traffic information for a circular region centering on the UHF roadside apparatus and traffic information for a doughnut-shaped region (292, 293) surrounding the circular region, in a time-division manner using UHF waves having the same frequency, and wherein the first UHF roadside apparatus has regions including a farthest-distance region farthest from the first UHF roadside apparatus and the second UHF roadside apparatus has regions including a farthest-distance region farthest from the second UHF roadside apparatus, wherein the farthest-distance region of the first UHF roadside apparatus and the farthest-distance region of the second UHF roadside apparatus overlap partially, and wherein the UHF transmission part of the first UHF roadside apparatus is adapted to transmit a UHF wave for the farthest-distance region of the first UHF roadside apparatus in a time different from a time where the UHF transmission part of the second UHF roadside apparatus is adapted to transmit a UHF wave for the farthest region of the second UHF roadside apparatus, and wherein the in-vehicle unit mounted in the vehicle includes: - a UHF reception part which receives the UHF wave transmitted by the UHF roadside apparatus; - a position specifying part which specifies a position of the vehicle; - a region specifying part which specifies a region where the vehicle is located, of the circular region and the doughnut-shaped region (292, 293), based on the position of the vehicle specified by the position specifying part; - a UHF selection part which selects, of the UHF wave received by the UHF reception part, a UHF wave received during a time assigned to the region specified by the region specifying part; and - a traffic information acquiring part which acquires traffic information from the UHF wave selected by the UHF selection part. a UHF transmission part which is adapted to transmit traffic information for a circular region centering on the UHF roadside apparatus and traffic information for a doughnut-shaped region (292, 293) surrounding the circular region, in a time-division manner using UHF waves having the same frequency, and wherein the first UHF roadside apparatus has regions including a farthest-distance region farthest from the first UHF roadside apparatus and the second UHF roadside apparatus has regions including a farthest-distance region farthest from the second UHF roadside apparatus, wherein the farthest-distance region of the first UHF roadside apparatus and the farthest-distance region of the second UHF roadside apparatus overlap partially, and wherein the UHF transmission part of the first UHF roadside apparatus is adapted to transmit a UHF wave for the farthest-distance region of the first UHF roadside apparatus in a time different from a time where the UHF transmission part of the second UHF roadside apparatus is adapted to transmit a UHF wave for the farthest region of the second UHF roadside apparatus, and wherein the in-vehicle unit mounted in the vehicle includes: - a UHF reception part which receives the UHF wave transmitted by the UHF roadside apparatus; - a position specifying part which specifies a position of the vehicle; - a region specifying part which specifies a region where the vehicle is located, of the circular region and the doughnut-shaped region (292, 293), based on the position of the vehicle specified by the position specifying part; - a UHF selection part which selects, of the UHF wave received by the UHF reception part, a UHF wave received during a time assigned to the region specified by the region specifying part; and - a traffic information acquiring part which acquires traffic information from the UHF wave selected by the UHF selection part. - a UHF reception part which receives the UHF wave transmitted by the UHF roadside apparatus; - a position specifying part which specifies a position of the vehicle; - a region specifying part which specifies a region where the vehicle is located, of the circular region and the doughnut-shaped region (292, 293), based on the position of the vehicle specified by the position specifying part; - a UHF selection part which selects, of the UHF wave received by the UHF reception part, a UHF wave received during a time assigned to the region specified by the region specifying part; and - a traffic information acquiring part which acquires traffic information from the UHF wave selected by the UHF selection part.